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 $67.76   12.543%   $76.2591   $76.26   $76.25   $76.30  
  Purchase #2 $216.38   3.725%   $224.4402   $224.44   $224.45   $224.40  
  Purchase #3 $47.68   12.139%   $53.4679   $53.47   $53.45   $53.50  
  Purchase #4 $197.70   3.689%   $204.9932   $204.99   $205.00   $205.00  
  Purchase #5 $132.42   5.272%   $139.4012   $139.40   $139.40   $139.40  
  Purchase #6 $88.90   4.760%   $93.1316   $93.13   $93.15   $93.10  
  Purchase #7 $150.77   12.848%   $170.1409   $170.14   $170.15   $170.10  
  7 purchase totals = $901.61       $961.8341   $961.83   $961.85   $961.80