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 $129.70   13.118%   $146.714   $146.71   $146.70   $146.70  
  Purchase #2 $49.30   10.114%   $54.2862   $54.29   $54.30   $54.30  
  Purchase #3 $76.69   7.739%   $82.625   $82.63   $82.65   $82.60  
  Purchase #4 $107.26   3.105%   $110.5904   $110.59   $110.60   $110.60  
  Purchase #5 $178.89   5.526%   $188.7755   $188.78   $188.80   $188.80  
  Purchase #6 $169.84   4.449%   $177.3962   $177.40   $177.40   $177.40  
  Purchase #7 $40.94   3.166%   $42.2362   $42.24   $42.25   $42.20  
  7 purchase totals = $752.62       $802.6235   $802.64   $802.70   $802.60