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 $62.28   5.246%   $65.5472   $65.55   $65.55   $65.50  
  Purchase #2 $250.84   7.304%   $269.1614   $269.16   $269.15   $269.20  
  Purchase #3 $192.81   10.812%   $213.6566   $213.66   $213.65   $213.70  
  Purchase #4 $136.67   4.866%   $143.3204   $143.32   $143.30   $143.30  
  Purchase #5 $5.47   7.151%   $5.8612   $5.86   $5.85   $5.90  
  Purchase #6 $44.50   13.238%   $50.3909   $50.39   $50.40   $50.40  
  Purchase #7 $166.77   9.323%   $182.318   $182.32   $182.30   $182.30  
  7 purchase totals = $859.34       $930.2557   $930.26   $930.20   $930.30