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 $22.46   7.123%   $24.0598   $24.06   $24.05   $24.10  
  Purchase #2 $152.37   6.442%   $162.1857   $162.19   $162.20   $162.20  
  Purchase #3 $14.98   8.840%   $16.3042   $16.30   $16.30   $16.30  
  Purchase #4 $182.47   4.612%   $190.8855   $190.89   $190.90   $190.90  
  Purchase #5 $37.87   5.820%   $40.074   $40.07   $40.05   $40.10  
  Purchase #6 $116.45   8.746%   $126.6347   $126.63   $126.65   $126.60  
  Purchase #7 $97.43   11.130%   $108.274   $108.27   $108.25   $108.30  
  7 purchase totals = $624.03       $668.4179   $668.41   $668.40   $668.50