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 $242.85   9.266%   $265.3525   $265.35   $265.35   $265.40  
  Purchase #2 $8.37   11.676%   $9.3473   $9.35   $9.35   $9.30  
  Purchase #3 $65.49   5.178%   $68.8811   $68.88   $68.90   $68.90  
  Purchase #4 $214.75   3.346%   $221.9355   $221.94   $221.95   $221.90  
  Purchase #5 $55.80   10.401%   $61.6038   $61.60   $61.60   $61.60  
  Purchase #6 $146.47   11.836%   $163.8062   $163.81   $163.80   $163.80  
  Purchase #7 $149.46   3.142%   $154.156   $154.16   $154.15   $154.20  
  7 purchase totals = $883.19       $945.0824   $945.09   $945.10   $945.10