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 $191.49   8.427%   $207.6269   $207.63   $207.65   $207.60  
  Purchase #2 $242.92   13.670%   $276.1272   $276.13   $276.15   $276.10  
  Purchase #3 $188.41   13.131%   $213.1501   $213.15   $213.15   $213.20  
  Purchase #4 $216.54   6.857%   $231.3881   $231.39   $231.40   $231.40  
  Purchase #5 $5.82   12.663%   $6.557   $6.56   $6.55   $6.60  
  Purchase #6 $248.67   5.200%   $261.6008   $261.60   $261.60   $261.60  
  Purchase #7 $194.55   8.272%   $210.6432   $210.64   $210.65   $210.60  
  7 purchase totals = $1,288.40       $1,407.0933   $1,407.10   $1,407.15   $1,407.10