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 $190.53   12.804%   $214.9255   $214.93   $214.95   $214.90  
  Purchase #2 $44.35   13.427%   $50.3049   $50.30   $50.30   $50.30  
  Purchase #3 $162.46   8.197%   $175.7768   $175.78   $175.80   $175.80  
  Purchase #4 $160.91   5.422%   $169.6345   $169.63   $169.65   $169.60  
  Purchase #5 $231.26   4.135%   $240.8226   $240.82   $240.80   $240.80  
  Purchase #6 $196.26   12.849%   $221.4774   $221.48   $221.50   $221.50  
  Purchase #7 $144.38   10.291%   $159.2381   $159.24   $159.25   $159.20  
  7 purchase totals = $1,130.15       $1,232.1798   $1,232.18   $1,232.25   $1,232.10