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 $119.25   6.296%   $126.758   $126.76   $126.75   $126.80  
  Purchase #2 $19.75   13.408%   $22.3981   $22.40   $22.40   $22.40  
  Purchase #3 $195.97   5.484%   $206.717   $206.72   $206.70   $206.70  
  Purchase #4 $141.88   11.785%   $158.6006   $158.60   $158.60   $158.60  
  Purchase #5 $196.32   7.468%   $210.9812   $210.98   $211.00   $211.00  
  Purchase #6 $58.75   3.115%   $60.5801   $60.58   $60.60   $60.60  
  Purchase #7 $22.31   4.660%   $23.3496   $23.35   $23.35   $23.30  
  7 purchase totals = $754.23       $809.3846   $809.39   $809.40   $809.40