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 $114.31   4.271%   $119.1922   $119.19   $119.20   $119.20  
  Purchase #2 $154.77   7.194%   $165.9042   $165.90   $165.90   $165.90  
  Purchase #3 $95.76   5.481%   $101.0086   $101.01   $101.00   $101.00  
  Purchase #4 $247.26   11.422%   $275.502   $275.50   $275.50   $275.50  
  Purchase #5 $20.36   6.156%   $21.6134   $21.61   $21.60   $21.60  
  Purchase #6 $151.91   12.302%   $170.598   $170.60   $170.60   $170.60  
  Purchase #7 $101.95   3.269%   $105.2827   $105.28   $105.30   $105.30  
  7 purchase totals = $886.32       $959.1011   $959.09   $959.10   $959.10