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 $176.27   3.589%   $182.5963   $182.60   $182.60   $182.60  
  Purchase #2 $122.39   11.566%   $136.5456   $136.55   $136.55   $136.50  
  Purchase #3 $52.30   3.199%   $53.9731   $53.97   $53.95   $54.00  
  Purchase #4 $194.59   4.535%   $203.4147   $203.41   $203.40   $203.40  
  Purchase #5 $222.59   11.126%   $247.3554   $247.36   $247.35   $247.40  
  Purchase #6 $184.46   11.378%   $205.4479   $205.45   $205.45   $205.40  
  Purchase #7 $212.67   13.607%   $241.608   $241.61   $241.60   $241.60  
  7 purchase totals = $1,165.27       $1,270.9410   $1,270.95   $1,270.90   $1,270.90