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 $233.79   12.619%   $263.292   $263.29   $263.30   $263.30  
  Purchase #2 $45.82   6.334%   $48.7222   $48.72   $48.70   $48.70  
  Purchase #3 $240.97   8.516%   $261.491   $261.49   $261.50   $261.50  
  Purchase #4 $236.41   12.551%   $266.0818   $266.08   $266.10   $266.10  
  Purchase #5 $99.61   3.821%   $103.4161   $103.42   $103.40   $103.40  
  Purchase #6 $248.38   12.643%   $279.7827   $279.78   $279.80   $279.80  
  Purchase #7 $218.51   9.824%   $239.9764   $239.98   $240.00   $240.00  
  7 purchase totals = $1,323.49       $1,462.7622   $1,462.76   $1,462.80   $1,462.80