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 $248.84   6.754%   $265.6467   $265.65   $265.65   $265.60  
  Purchase #2 $225.26   8.747%   $244.9635   $244.96   $244.95   $245.00  
  Purchase #3 $11.35   3.385%   $11.7342   $11.73   $11.75   $11.70  
  Purchase #4 $64.84   7.138%   $69.4683   $69.47   $69.45   $69.50  
  Purchase #5 $17.87   11.387%   $19.9049   $19.90   $19.90   $19.90  
  Purchase #6 $195.68   6.774%   $208.9354   $208.94   $208.95   $208.90  
  Purchase #7 $108.25   3.370%   $111.898   $111.90   $111.90   $111.90  
  7 purchase totals = $872.09       $932.5510   $932.55   $932.55   $932.50