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 $246.84   5.860%   $261.3048   $261.30   $261.30   $261.30  
  Purchase #2 $73.32   4.301%   $76.4735   $76.47   $76.45   $76.50  
  Purchase #3 $9.28   9.456%   $10.1575   $10.16   $10.15   $10.20  
  Purchase #4 $10.25   7.467%   $11.0154   $11.02   $11.00   $11.00  
  Purchase #5 $158.71   5.268%   $167.0708   $167.07   $167.05   $167.10  
  Purchase #6 $123.68   9.643%   $135.6065   $135.61   $135.60   $135.60  
  Purchase #7 $106.44   4.132%   $110.8381   $110.84   $110.85   $110.80  
  7 purchase totals = $728.52       $772.4666   $772.47   $772.40   $772.50