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 $112.52   11.116%   $125.0277   $125.03   $125.05   $125.00  
  Purchase #2 $64.39   3.176%   $66.435   $66.44   $66.45   $66.40  
  Purchase #3 $214.29   7.872%   $231.1589   $231.16   $231.15   $231.20  
  Purchase #4 $200.66   13.431%   $227.6106   $227.61   $227.60   $227.60  
  Purchase #5 $58.46   10.304%   $64.4837   $64.48   $64.50   $64.50  
  Purchase #6 $147.55   13.250%   $167.1004   $167.10   $167.10   $167.10  
  Purchase #7 $6.92   3.526%   $7.164   $7.16   $7.15   $7.20  
  7 purchase totals = $804.79       $888.9803   $888.98   $889.00   $889.00