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 $214.74   6.242%   $228.1441   $228.14   $228.15   $228.10  
  Purchase #2 $40.49   13.448%   $45.9351   $45.94   $45.95   $45.90  
  Purchase #3 $115.99   13.203%   $131.3042   $131.30   $131.30   $131.30  
  Purchase #4 $71.35   9.192%   $77.9085   $77.91   $77.90   $77.90  
  Purchase #5 $146.80   8.369%   $159.0857   $159.09   $159.10   $159.10  
  Purchase #6 $193.33   10.210%   $213.069   $213.07   $213.05   $213.10  
  Purchase #7 $157.91   6.834%   $168.7016   $168.70   $168.70   $168.70  
  7 purchase totals = $940.61       $1,024.1482   $1,024.15   $1,024.15   $1,024.10