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 $24.37   8.488%   $26.4385   $26.44   $26.45   $26.40  
  Purchase #2 $16.53   9.487%   $18.0982   $18.10   $18.10   $18.10  
  Purchase #3 $60.75   9.461%   $66.4976   $66.50   $66.50   $66.50  
  Purchase #4 $141.53   3.584%   $146.6024   $146.60   $146.60   $146.60  
  Purchase #5 $91.48   4.652%   $95.7356   $95.74   $95.75   $95.70  
  Purchase #6 $163.75   5.650%   $173.0019   $173.00   $173.00   $173.00  
  Purchase #7 $213.69   11.369%   $237.9844   $237.98   $238.00   $238.00  
  7 purchase totals = $712.10       $764.3586   $764.36   $764.40   $764.30