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 $86.79   9.680%   $95.1913   $95.19   $95.20   $95.20  
  Purchase #2 $134.78   10.766%   $149.2904   $149.29   $149.30   $149.30  
  Purchase #3 $118.36   7.517%   $127.2571   $127.26   $127.25   $127.30  
  Purchase #4 $190.73   9.804%   $209.4292   $209.43   $209.45   $209.40  
  Purchase #5 $125.95   5.805%   $133.2614   $133.26   $133.25   $133.30  
  Purchase #6 $101.43   5.431%   $106.9387   $106.94   $106.95   $106.90  
  Purchase #7 $148.78   8.818%   $161.8994   $161.90   $161.90   $161.90  
  7 purchase totals = $906.82       $983.2675   $983.27   $983.30   $983.30