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 $238.57   11.455%   $265.8982   $265.90   $265.90   $265.90  
  Purchase #2 $147.99   4.361%   $154.4438   $154.44   $154.45   $154.40  
  Purchase #3 $197.68   5.223%   $208.0048   $208.00   $208.00   $208.00  
  Purchase #4 $68.42   12.133%   $76.7214   $76.72   $76.70   $76.70  
  Purchase #5 $89.87   6.814%   $95.9937   $95.99   $96.00   $96.00  
  Purchase #6 $84.61   9.375%   $92.5422   $92.54   $92.55   $92.50  
  Purchase #7 $124.98   5.826%   $132.2613   $132.26   $132.25   $132.30  
  7 purchase totals = $952.12       $1,025.8654   $1,025.85   $1,025.85   $1,025.80