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 $207.58   5.164%   $218.2994   $218.30   $218.30   $218.30  
  Purchase #2 $114.31   3.664%   $118.4983   $118.50   $118.50   $118.50  
  Purchase #3 $47.48   8.664%   $51.5937   $51.59   $51.60   $51.60  
  Purchase #4 $133.64   13.570%   $151.7749   $151.77   $151.75   $151.80  
  Purchase #5 $205.44   13.731%   $233.649   $233.65   $233.65   $233.60  
  Purchase #6 $51.27   5.145%   $53.9078   $53.91   $53.90   $53.90  
  Purchase #7 $232.28   12.678%   $261.7285   $261.73   $261.75   $261.70  
  7 purchase totals = $992.00       $1,089.4516   $1,089.45   $1,089.45   $1,089.40