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 $57.89   13.350%   $65.6183   $65.62   $65.60   $65.60  
  Purchase #2 $46.70   10.291%   $51.5059   $51.51   $51.50   $51.50  
  Purchase #3 $88.82   5.258%   $93.4902   $93.49   $93.50   $93.50  
  Purchase #4 $208.80   5.601%   $220.4949   $220.49   $220.50   $220.50  
  Purchase #5 $5.74   5.430%   $6.0517   $6.05   $6.05   $6.10  
  Purchase #6 $205.42   10.561%   $227.1144   $227.11   $227.10   $227.10  
  Purchase #7 $104.96   12.361%   $117.9341   $117.93   $117.95   $117.90  
  7 purchase totals = $718.33       $782.2095   $782.20   $782.20   $782.20