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 $71.53   6.719%   $76.3361   $76.34   $76.35   $76.30  
  Purchase #2 $194.32   8.473%   $210.7847   $210.78   $210.80   $210.80  
  Purchase #3 $78.87   7.674%   $84.9225   $84.92   $84.90   $84.90  
  Purchase #4 $197.97   8.349%   $214.4985   $214.50   $214.50   $214.50  
  Purchase #5 $112.55   9.631%   $123.3897   $123.39   $123.40   $123.40  
  Purchase #6 $16.39   3.862%   $17.023   $17.02   $17.00   $17.00  
  Purchase #7 $238.29   6.754%   $254.3841   $254.38   $254.40   $254.40  
  7 purchase totals = $909.92       $981.3386   $981.33   $981.35   $981.30