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 $48.26   8.774%   $52.4943   $52.49   $52.50   $52.50  
  Purchase #2 $115.35   6.403%   $122.7359   $122.74   $122.75   $122.70  
  Purchase #3 $195.37   13.405%   $221.5593   $221.56   $221.55   $221.60  
  Purchase #4 $68.32   6.108%   $72.493   $72.49   $72.50   $72.50  
  Purchase #5 $68.28   6.763%   $72.8978   $72.90   $72.90   $72.90  
  Purchase #6 $101.40   12.859%   $114.439   $114.44   $114.45   $114.40  
  Purchase #7 $118.43   6.386%   $125.9929   $125.99   $126.00   $126.00  
  7 purchase totals = $715.41       $782.6122   $782.61   $782.65   $782.60