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 $223.56   11.754%   $249.8372   $249.84   $249.85   $249.80  
  Purchase #2 $229.65   10.755%   $254.3489   $254.35   $254.35   $254.30  
  Purchase #3 $148.91   9.660%   $163.2947   $163.29   $163.30   $163.30  
  Purchase #4 $167.74   8.788%   $182.481   $182.48   $182.50   $182.50  
  Purchase #5 $245.97   13.785%   $279.877   $279.88   $279.90   $279.90  
  Purchase #6 $129.94   8.191%   $140.5834   $140.58   $140.60   $140.60  
  Purchase #7 $209.91   12.189%   $235.4959   $235.50   $235.50   $235.50  
  7 purchase totals = $1,355.68       $1,505.9181   $1,505.92   $1,506.00   $1,505.90