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 $67.49   12.796%   $76.126   $76.13   $76.15   $76.10  
  Purchase #2 $58.48   8.221%   $63.2876   $63.29   $63.30   $63.30  
  Purchase #3 $216.79   5.159%   $227.9742   $227.97   $227.95   $228.00  
  Purchase #4 $43.54   3.743%   $45.1697   $45.17   $45.15   $45.20  
  Purchase #5 $111.40   11.656%   $124.3848   $124.38   $124.40   $124.40  
  Purchase #6 $217.31   11.236%   $241.727   $241.73   $241.75   $241.70  
  Purchase #7 $46.65   3.338%   $48.2072   $48.21   $48.20   $48.20  
  7 purchase totals = $761.66       $826.8765   $826.88   $826.90   $826.90