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 $219.67   5.586%   $231.9408   $231.94   $231.95   $231.90  
  Purchase #2 $185.72   5.776%   $196.4472   $196.45   $196.45   $196.40  
  Purchase #3 $118.44   5.328%   $124.7505   $124.75   $124.75   $124.80  
  Purchase #4 $96.38   11.291%   $107.2623   $107.26   $107.25   $107.30  
  Purchase #5 $147.98   4.779%   $155.052   $155.05   $155.05   $155.10  
  Purchase #6 $116.62   6.336%   $124.009   $124.01   $124.00   $124.00  
  Purchase #7 $235.73   9.857%   $258.9659   $258.97   $258.95   $259.00  
  7 purchase totals = $1,120.54       $1,198.4277   $1,198.43   $1,198.40   $1,198.50