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 $114.44   10.324%   $126.2548   $126.25   $126.25   $126.30  
  Purchase #2 $176.58   4.105%   $183.8286   $183.83   $183.85   $183.80  
  Purchase #3 $103.81   7.316%   $111.4047   $111.40   $111.40   $111.40  
  Purchase #4 $61.72   8.779%   $67.1384   $67.14   $67.15   $67.10  
  Purchase #5 $244.43   4.775%   $256.1015   $256.10   $256.10   $256.10  
  Purchase #6 $129.56   4.790%   $135.7659   $135.77   $135.75   $135.80  
  Purchase #7 $41.69   5.502%   $43.9838   $43.98   $44.00   $44.00  
  7 purchase totals = $872.23       $924.4777   $924.47   $924.50   $924.50