Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $218.89   12.568%   $246.4001   $246.40   $246.40   $246.40  
  Purchase #2 $194.95   5.529%   $205.7288   $205.73   $205.75   $205.70  
  Purchase #3 $101.65   12.621%   $114.4792   $114.48   $114.50   $114.50  
  Purchase #4 $247.27   13.722%   $281.2004   $281.20   $281.20   $281.20  
  Purchase #5 $181.90   13.788%   $206.9804   $206.98   $207.00   $207.00  
  Purchase #6 $235.75   13.481%   $267.5315   $267.53   $267.55   $267.50  
  Purchase #7 $227.68   10.579%   $251.7663   $251.77   $251.75   $251.80  
  7 purchase totals = $1,408.09       $1,574.0867   $1,574.09   $1,574.15   $1,574.10