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 $119.32   5.779%   $126.2155   $126.22   $126.20   $126.20  
  Purchase #2 $18.54   8.764%   $20.1648   $20.16   $20.15   $20.20  
  Purchase #3 $200.47   3.838%   $208.164   $208.16   $208.15   $208.20  
  Purchase #4 $131.65   9.584%   $144.2673   $144.27   $144.25   $144.30  
  Purchase #5 $49.42   10.770%   $54.7425   $54.74   $54.75   $54.70  
  Purchase #6 $195.47   5.414%   $206.0527   $206.05   $206.05   $206.10  
  Purchase #7 $86.31   12.176%   $96.8191   $96.82   $96.80   $96.80  
  7 purchase totals = $801.18       $856.4259   $856.42   $856.35   $856.50