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 $63.76   3.827%   $66.2001   $66.20   $66.20   $66.20  
  Purchase #2 $156.98   7.324%   $168.4772   $168.48   $168.50   $168.50  
  Purchase #3 $239.49   12.861%   $270.2908   $270.29   $270.30   $270.30  
  Purchase #4 $168.77   12.717%   $190.2325   $190.23   $190.25   $190.20  
  Purchase #5 $16.59   11.204%   $18.4487   $18.45   $18.45   $18.40  
  Purchase #6 $178.67   9.264%   $195.222   $195.22   $195.20   $195.20  
  Purchase #7 $49.90   10.809%   $55.2937   $55.29   $55.30   $55.30  
  7 purchase totals = $874.16       $964.1650   $964.16   $964.20   $964.10