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 $112.51   11.297%   $125.2203   $125.22   $125.20   $125.20  
  Purchase #2 $11.64   9.106%   $12.6999   $12.70   $12.70   $12.70  
  Purchase #3 $123.67   7.519%   $132.9687   $132.97   $132.95   $133.00  
  Purchase #4 $238.74   11.671%   $266.6033   $266.60   $266.60   $266.60  
  Purchase #5 $44.88   10.146%   $49.4335   $49.43   $49.45   $49.40  
  Purchase #6 $163.50   7.575%   $175.8851   $175.89   $175.90   $175.90  
  Purchase #7 $60.75   12.425%   $68.2982   $68.30   $68.30   $68.30  
  7 purchase totals = $755.69       $831.1090   $831.11   $831.10   $831.10