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 $66.82   12.639%   $75.2654   $75.27   $75.25   $75.30  
  Purchase #2 $109.70   7.842%   $118.3027   $118.30   $118.30   $118.30  
  Purchase #3 $153.28   5.675%   $161.9786   $161.98   $162.00   $162.00  
  Purchase #4 $229.99   11.140%   $255.6109   $255.61   $255.60   $255.60  
  Purchase #5 $93.29   7.114%   $99.9267   $99.93   $99.95   $99.90  
  Purchase #6 $14.86   10.565%   $16.43   $16.43   $16.45   $16.40  
  Purchase #7 $96.53   5.539%   $101.8768   $101.88   $101.90   $101.90  
  7 purchase totals = $764.47       $829.3911   $829.40   $829.45   $829.40