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 $59.34   13.472%   $67.3343   $67.33   $67.35   $67.30  
  Purchase #2 $105.39   7.624%   $113.4249   $113.42   $113.40   $113.40  
  Purchase #3 $215.80   9.596%   $236.5082   $236.51   $236.50   $236.50  
  Purchase #4 $28.31   9.207%   $30.9165   $30.92   $30.90   $30.90  
  Purchase #5 $217.82   11.556%   $242.9913   $242.99   $243.00   $243.00  
  Purchase #6 $226.84   13.813%   $258.1734   $258.17   $258.15   $258.20  
  Purchase #7 $9.38   13.659%   $10.6612   $10.66   $10.65   $10.70  
  7 purchase totals = $862.88       $960.0098   $960.00   $959.95   $960.00