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 $119.63   5.482%   $126.1881   $126.19   $126.20   $126.20  
  Purchase #2 $104.74   10.428%   $115.6623   $115.66   $115.65   $115.70  
  Purchase #3 $115.84   9.414%   $126.7452   $126.75   $126.75   $126.70  
  Purchase #4 $55.80   8.185%   $60.3672   $60.37   $60.35   $60.40  
  Purchase #5 $160.57   5.480%   $169.3692   $169.37   $169.35   $169.40  
  Purchase #6 $25.31   3.756%   $26.2606   $26.26   $26.25   $26.30  
  Purchase #7 $134.45   8.682%   $146.1229   $146.12   $146.10   $146.10  
  7 purchase totals = $716.34       $770.7155   $770.72   $770.65   $770.80