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 $240.88   11.428%   $268.4078   $268.41   $268.40   $268.40  
  Purchase #2 $58.27   7.558%   $62.674   $62.67   $62.65   $62.70  
  Purchase #3 $176.78   10.811%   $195.8917   $195.89   $195.90   $195.90  
  Purchase #4 $108.87   11.768%   $121.6818   $121.68   $121.70   $121.70  
  Purchase #5 $233.26   12.237%   $261.804   $261.80   $261.80   $261.80  
  Purchase #6 $101.82   3.351%   $105.232   $105.23   $105.25   $105.20  
  Purchase #7 $191.41   9.546%   $209.682   $209.68   $209.70   $209.70  
  7 purchase totals = $1,111.29       $1,225.3733   $1,225.36   $1,225.40   $1,225.40