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 $58.69   12.719%   $66.1548   $66.15   $66.15   $66.20  
  Purchase #2 $236.97   3.517%   $245.3042   $245.30   $245.30   $245.30  
  Purchase #3 $146.51   10.481%   $161.8657   $161.87   $161.85   $161.90  
  Purchase #4 $107.71   4.507%   $112.5645   $112.56   $112.55   $112.60  
  Purchase #5 $225.79   6.132%   $239.6354   $239.64   $239.65   $239.60  
  Purchase #6 $242.60   4.358%   $253.1725   $253.17   $253.15   $253.20  
  Purchase #7 $24.92   3.290%   $25.7399   $25.74   $25.75   $25.70  
  7 purchase totals = $1,043.19       $1,104.4370   $1,104.43   $1,104.40   $1,104.50