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 $248.66   10.702%   $275.2716   $275.27   $275.25   $275.30  
  Purchase #2 $192.62   13.327%   $218.2905   $218.29   $218.30   $218.30  
  Purchase #3 $157.75   11.725%   $176.2462   $176.25   $176.25   $176.20  
  Purchase #4 $233.83   11.709%   $261.2092   $261.21   $261.20   $261.20  
  Purchase #5 $60.41   9.394%   $66.0849   $66.08   $66.10   $66.10  
  Purchase #6 $76.36   10.711%   $84.5389   $84.54   $84.55   $84.50  
  Purchase #7 $84.74   6.791%   $90.4947   $90.49   $90.50   $90.50  
  7 purchase totals = $1,054.37       $1,172.1360   $1,172.13   $1,172.15   $1,172.10