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 $249.38   7.283%   $267.5423   $267.54   $267.55   $267.50  
  Purchase #2 $177.87   9.629%   $194.9971   $195.00   $195.00   $195.00  
  Purchase #3 $122.47   5.646%   $129.3847   $129.38   $129.40   $129.40  
  Purchase #4 $94.34   3.568%   $97.7061   $97.71   $97.70   $97.70  
  Purchase #5 $16.26   10.637%   $17.9896   $17.99   $18.00   $18.00  
  Purchase #6 $155.34   5.640%   $164.1012   $164.10   $164.10   $164.10  
  Purchase #7 $154.90   9.691%   $169.9114   $169.91   $169.90   $169.90  
  7 purchase totals = $970.56       $1,041.6324   $1,041.63   $1,041.65   $1,041.60