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 $154.42   9.154%   $168.5556   $168.56   $168.55   $168.60  
  Purchase #2 $76.82   10.356%   $84.7755   $84.78   $84.80   $84.80  
  Purchase #3 $72.77   8.428%   $78.9031   $78.90   $78.90   $78.90  
  Purchase #4 $119.97   8.629%   $130.3222   $130.32   $130.30   $130.30  
  Purchase #5 $184.51   8.195%   $199.6306   $199.63   $199.65   $199.60  
  Purchase #6 $218.48   3.626%   $226.4021   $226.40   $226.40   $226.40  
  Purchase #7 $58.33   13.819%   $66.3906   $66.39   $66.40   $66.40  
  7 purchase totals = $885.30       $954.9797   $954.98   $955.00   $955.00