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 $205.41   13.559%   $233.2615   $233.26   $233.25   $233.30  
  Purchase #2 $126.39   8.485%   $137.1142   $137.11   $137.10   $137.10  
  Purchase #3 $249.31   9.306%   $272.5108   $272.51   $272.50   $272.50  
  Purchase #4 $98.64   13.774%   $112.2267   $112.23   $112.25   $112.20  
  Purchase #5 $49.72   8.545%   $53.9686   $53.97   $53.95   $54.00  
  Purchase #6 $237.48   4.637%   $248.4919   $248.49   $248.50   $248.50  
  Purchase #7 $219.39   5.261%   $230.9321   $230.93   $230.95   $230.90  
  7 purchase totals = $1,186.34       $1,288.5058   $1,288.50   $1,288.50   $1,288.50