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 $214.38   3.136%   $221.103   $221.10   $221.10   $221.10  
  Purchase #2 $182.26   9.342%   $199.2867   $199.29   $199.30   $199.30  
  Purchase #3 $93.96   9.316%   $102.7133   $102.71   $102.70   $102.70  
  Purchase #4 $29.98   11.648%   $33.4721   $33.47   $33.45   $33.50  
  Purchase #5 $165.62   7.681%   $178.3413   $178.34   $178.35   $178.30  
  Purchase #6 $71.67   7.249%   $76.8654   $76.87   $76.85   $76.90  
  Purchase #7 $210.68   5.223%   $221.6838   $221.68   $221.70   $221.70  
  7 purchase totals = $968.55       $1,033.4656   $1,033.46   $1,033.45   $1,033.50