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 $24.50   6.525%   $26.0986   $26.10   $26.10   $26.10  
  Purchase #2 $180.96   11.863%   $202.4273   $202.43   $202.45   $202.40  
  Purchase #3 $41.78   13.414%   $47.3844   $47.38   $47.40   $47.40  
  Purchase #4 $108.58   6.650%   $115.8006   $115.80   $115.80   $115.80  
  Purchase #5 $180.86   10.512%   $199.872   $199.87   $199.85   $199.90  
  Purchase #6 $53.38   8.424%   $57.8767   $57.88   $57.90   $57.90  
  Purchase #7 $88.87   6.109%   $94.2991   $94.30   $94.30   $94.30  
  7 purchase totals = $678.93       $743.7587   $743.76   $743.80   $743.80