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 $23.46   5.614%   $24.777   $24.78   $24.80   $24.80  
  Purchase #2 $13.27   9.231%   $14.495   $14.50   $14.50   $14.50  
  Purchase #3 $159.89   10.316%   $176.3843   $176.38   $176.40   $176.40  
  Purchase #4 $22.61   8.626%   $24.5603   $24.56   $24.55   $24.60  
  Purchase #5 $169.97   3.481%   $175.8867   $175.89   $175.90   $175.90  
  Purchase #6 $149.25   5.738%   $157.814   $157.81   $157.80   $157.80  
  Purchase #7 $215.46   12.553%   $242.5067   $242.51   $242.50   $242.50  
  7 purchase totals = $753.91       $816.4240   $816.43   $816.45   $816.50