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 $236.82   4.197%   $246.7593   $246.76   $246.75   $246.80  
  Purchase #2 $21.84   13.113%   $24.7039   $24.70   $24.70   $24.70  
  Purchase #3 $62.35   3.767%   $64.6987   $64.70   $64.70   $64.70  
  Purchase #4 $32.96   10.683%   $36.4811   $36.48   $36.50   $36.50  
  Purchase #5 $164.66   9.781%   $180.7654   $180.77   $180.75   $180.80  
  Purchase #6 $246.65   6.455%   $262.5713   $262.57   $262.55   $262.60  
  Purchase #7 $112.53   9.462%   $123.1776   $123.18   $123.20   $123.20  
  7 purchase totals = $877.81       $939.1573   $939.16   $939.15   $939.30