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 $238.29   9.611%   $261.1921   $261.19   $261.20   $261.20  
  Purchase #2 $103.86   12.652%   $117.0004   $117.00   $117.00   $117.00  
  Purchase #3 $117.62   7.663%   $126.6332   $126.63   $126.65   $126.60  
  Purchase #4 $92.78   9.505%   $101.5987   $101.60   $101.60   $101.60  
  Purchase #5 $154.86   5.580%   $163.5012   $163.50   $163.50   $163.50  
  Purchase #6 $244.95   3.153%   $252.6733   $252.67   $252.65   $252.70  
  Purchase #7 $200.99   13.256%   $227.6332   $227.63   $227.65   $227.60  
  7 purchase totals = $1,153.35       $1,250.2321   $1,250.22   $1,250.25   $1,250.20