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 $241.82   8.429%   $262.203   $262.20   $262.20   $262.20  
  Purchase #2 $117.79   12.691%   $132.7387   $132.74   $132.75   $132.70  
  Purchase #3 $229.48   11.714%   $256.3613   $256.36   $256.35   $256.40  
  Purchase #4 $196.26   7.219%   $210.428   $210.43   $210.45   $210.40  
  Purchase #5 $32.76   8.195%   $35.4447   $35.44   $35.45   $35.40  
  Purchase #6 $60.78   8.740%   $66.0922   $66.09   $66.10   $66.10  
  Purchase #7 $242.46   10.832%   $268.7233   $268.72   $268.70   $268.70  
  7 purchase totals = $1,121.35       $1,231.9912   $1,231.98   $1,232.00   $1,231.90