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 $47.69   11.754%   $53.2955   $53.30   $53.30   $53.30  
  Purchase #2 $169.73   7.295%   $182.1118   $182.11   $182.10   $182.10  
  Purchase #3 $116.41   4.235%   $121.34   $121.34   $121.35   $121.30  
  Purchase #4 $150.55   12.105%   $168.7741   $168.77   $168.75   $168.80  
  Purchase #5 $225.92   3.299%   $233.3731   $233.37   $233.35   $233.40  
  Purchase #6 $215.36   12.746%   $242.8098   $242.81   $242.80   $242.80  
  Purchase #7 $224.63   13.292%   $254.4878   $254.49   $254.50   $254.50  
  7 purchase totals = $1,150.29       $1,256.1921   $1,256.19   $1,256.15   $1,256.20