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 $119.96   4.837%   $125.7625   $125.76   $125.75   $125.80  
  Purchase #2 $93.61   13.707%   $106.4411   $106.44   $106.45   $106.40  
  Purchase #3 $29.60   11.226%   $32.9229   $32.92   $32.90   $32.90  
  Purchase #4 $233.74   13.846%   $266.1036   $266.10   $266.10   $266.10  
  Purchase #5 $68.95   3.158%   $71.1274   $71.13   $71.15   $71.10  
  Purchase #6 $246.38   11.309%   $274.2431   $274.24   $274.25   $274.20  
  Purchase #7 $20.25   3.105%   $20.8788   $20.88   $20.90   $20.90  
  7 purchase totals = $812.49       $897.4794   $897.47   $897.50   $897.40