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 $245.89   11.169%   $273.3535   $273.35   $273.35   $273.40  
  Purchase #2 $112.38   8.628%   $122.0761   $122.08   $122.10   $122.10  
  Purchase #3 $61.82   7.781%   $66.6302   $66.63   $66.65   $66.60  
  Purchase #4 $17.29   9.389%   $18.9134   $18.91   $18.90   $18.90  
  Purchase #5 $129.66   10.364%   $143.098   $143.10   $143.10   $143.10  
  Purchase #6 $245.99   5.681%   $259.9647   $259.96   $259.95   $260.00  
  Purchase #7 $59.26   12.733%   $66.8056   $66.81   $66.80   $66.80  
  7 purchase totals = $872.29       $950.8415   $950.84   $950.85   $950.90