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 $66.95   11.208%   $74.4538   $74.45   $74.45   $74.50  
  Purchase #2 $246.34   6.112%   $261.3963   $261.40   $261.40   $261.40  
  Purchase #3 $144.67   6.680%   $154.334   $154.33   $154.35   $154.30  
  Purchase #4 $176.25   5.750%   $186.3844   $186.38   $186.40   $186.40  
  Purchase #5 $166.74   8.206%   $180.4227   $180.42   $180.40   $180.40  
  Purchase #6 $230.82   7.564%   $248.2792   $248.28   $248.30   $248.30  
  Purchase #7 $141.37   7.175%   $151.5133   $151.51   $151.50   $151.50  
  7 purchase totals = $1,173.14       $1,256.7837   $1,256.77   $1,256.80   $1,256.80