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 $67.34   13.253%   $76.2646   $76.26   $76.25   $76.30  
  Purchase #2 $92.94   12.411%   $104.4748   $104.47   $104.45   $104.50  
  Purchase #3 $33.25   4.523%   $34.7539   $34.75   $34.75   $34.80  
  Purchase #4 $161.39   8.644%   $175.3406   $175.34   $175.35   $175.30  
  Purchase #5 $128.76   11.161%   $143.1309   $143.13   $143.15   $143.10  
  Purchase #6 $74.97   4.649%   $78.4554   $78.46   $78.45   $78.50  
  Purchase #7 $46.96   4.198%   $48.9314   $48.93   $48.95   $48.90  
  7 purchase totals = $605.61       $661.3516   $661.34   $661.35   $661.40