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 $20.87   11.525%   $23.2753   $23.28   $23.30   $23.30  
  Purchase #2 $159.54   10.350%   $176.0524   $176.05   $176.05   $176.10  
  Purchase #3 $57.34   10.384%   $63.2942   $63.29   $63.30   $63.30  
  Purchase #4 $62.48   7.497%   $67.1641   $67.16   $67.15   $67.20  
  Purchase #5 $64.50   13.184%   $73.0037   $73.00   $73.00   $73.00  
  Purchase #6 $233.83   3.257%   $241.4458   $241.45   $241.45   $241.40  
  Purchase #7 $119.26   3.227%   $123.1085   $123.11   $123.10   $123.10  
  7 purchase totals = $717.82       $767.3440   $767.34   $767.35   $767.40