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 $222.82   10.857%   $247.0116   $247.01   $247.00   $247.00  
  Purchase #2 $23.94   13.289%   $27.1214   $27.12   $27.10   $27.10  
  Purchase #3 $203.40   3.728%   $210.9828   $210.98   $211.00   $211.00  
  Purchase #4 $48.66   5.843%   $51.5032   $51.50   $51.50   $51.50  
  Purchase #5 $8.63   11.531%   $9.6251   $9.63   $9.65   $9.60  
  Purchase #6 $131.67   11.422%   $146.7093   $146.71   $146.70   $146.70  
  Purchase #7 $144.73   10.426%   $159.8195   $159.82   $159.80   $159.80  
  7 purchase totals = $783.85       $852.7729   $852.77   $852.75   $852.70