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 $112.39   12.660%   $126.6186   $126.62   $126.60   $126.60  
  Purchase #2 $155.78   9.291%   $170.2535   $170.25   $170.25   $170.30  
  Purchase #3 $10.60   3.258%   $10.9453   $10.95   $10.95   $10.90  
  Purchase #4 $95.89   10.401%   $105.8635   $105.86   $105.85   $105.90  
  Purchase #5 $123.46   9.872%   $135.648   $135.65   $135.65   $135.60  
  Purchase #6 $92.79   8.141%   $100.344   $100.34   $100.35   $100.30  
  Purchase #7 $144.79   3.346%   $149.6347   $149.63   $149.65   $149.60  
  7 purchase totals = $735.70       $799.3076   $799.30   $799.30   $799.20