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 $22.68   5.581%   $23.9458   $23.95   $23.95   $23.90  
  Purchase #2 $180.86   3.756%   $187.6531   $187.65   $187.65   $187.70  
  Purchase #3 $34.82   10.545%   $38.4918   $38.49   $38.50   $38.50  
  Purchase #4 $158.59   6.486%   $168.8761   $168.88   $168.90   $168.90  
  Purchase #5 $120.68   4.539%   $126.1577   $126.16   $126.15   $126.20  
  Purchase #6 $160.86   3.577%   $166.614   $166.61   $166.60   $166.60  
  Purchase #7 $215.73   4.265%   $224.9309   $224.93   $224.95   $224.90  
  7 purchase totals = $894.22       $936.6694   $936.67   $936.70   $936.70