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 $42.95   10.115%   $47.2944   $47.29   $47.30   $47.30  
  Purchase #2 $53.70   5.532%   $56.6707   $56.67   $56.65   $56.70  
  Purchase #3 $62.36   4.608%   $65.2335   $65.23   $65.25   $65.20  
  Purchase #4 $98.25   3.289%   $101.4814   $101.48   $101.50   $101.50  
  Purchase #5 $19.53   8.550%   $21.1998   $21.20   $21.20   $21.20  
  Purchase #6 $174.90   11.278%   $194.6252   $194.63   $194.65   $194.60  
  Purchase #7 $73.40   3.852%   $76.2274   $76.23   $76.25   $76.20  
  7 purchase totals = $525.09       $562.7324   $562.73   $562.80   $562.70