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 $184.57   13.569%   $209.6143   $209.61   $209.60   $209.60  
  Purchase #2 $217.43   11.598%   $242.6475   $242.65   $242.65   $242.60  
  Purchase #3 $41.97   13.462%   $47.62   $47.62   $47.60   $47.60  
  Purchase #4 $151.30   8.549%   $164.2346   $164.23   $164.25   $164.20  
  Purchase #5 $67.84   11.479%   $75.6274   $75.63   $75.65   $75.60  
  Purchase #6 $121.43   12.659%   $136.8018   $136.80   $136.80   $136.80  
  Purchase #7 $236.60   3.588%   $245.0892   $245.09   $245.10   $245.10  
  7 purchase totals = $1,021.14       $1,121.6348   $1,121.63   $1,121.65   $1,121.50