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 $88.53   11.417%   $98.6375   $98.64   $98.65   $98.60  
  Purchase #2 $233.64   10.158%   $257.3732   $257.37   $257.35   $257.40  
  Purchase #3 $51.79   9.664%   $56.795   $56.80   $56.80   $56.80  
  Purchase #4 $125.41   4.375%   $130.8967   $130.90   $130.90   $130.90  
  Purchase #5 $104.96   8.769%   $114.1639   $114.16   $114.15   $114.20  
  Purchase #6 $127.73   13.245%   $144.6478   $144.65   $144.65   $144.60  
  Purchase #7 $28.38   8.687%   $30.8454   $30.85   $30.85   $30.80  
  7 purchase totals = $760.44       $833.3595   $833.37   $833.35   $833.30