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 $164.55   6.534%   $175.3017   $175.30   $175.30   $175.30  
  Purchase #2 $102.81   9.483%   $112.5595   $112.56   $112.55   $112.60  
  Purchase #3 $22.56   13.156%   $25.528   $25.53   $25.55   $25.50  
  Purchase #4 $178.84   3.719%   $185.4911   $185.49   $185.50   $185.50  
  Purchase #5 $81.97   5.259%   $86.2808   $86.28   $86.30   $86.30  
  Purchase #6 $123.85   11.139%   $137.6457   $137.65   $137.65   $137.60  
  Purchase #7 $163.61   11.542%   $182.4939   $182.49   $182.50   $182.50  
  7 purchase totals = $838.19       $905.3007   $905.30   $905.35   $905.30