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 $236.79   10.746%   $262.2355   $262.24   $262.25   $262.20  
  Purchase #2 $147.98   5.512%   $156.1367   $156.14   $156.15   $156.10  
  Purchase #3 $82.68   7.608%   $88.9703   $88.97   $88.95   $89.00  
  Purchase #4 $101.38   13.397%   $114.9619   $114.96   $114.95   $115.00  
  Purchase #5 $95.44   11.515%   $106.4299   $106.43   $106.45   $106.40  
  Purchase #6 $144.38   9.422%   $157.9835   $157.98   $158.00   $158.00  
  Purchase #7 $175.74   5.707%   $185.7695   $185.77   $185.75   $185.80  
  7 purchase totals = $984.39       $1,072.4873   $1,072.49   $1,072.50   $1,072.50