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 $141.40   3.495%   $146.3419   $146.34   $146.35   $146.30  
  Purchase #2 $161.89   8.471%   $175.6037   $175.60   $175.60   $175.60  
  Purchase #3 $232.69   5.845%   $246.2907   $246.29   $246.30   $246.30  
  Purchase #4 $82.57   8.382%   $89.491   $89.49   $89.50   $89.50  
  Purchase #5 $89.25   7.563%   $96   $96.00   $96.00   $96.00  
  Purchase #6 $240.37   8.833%   $261.6019   $261.60   $261.60   $261.60  
  Purchase #7 $159.97   8.395%   $173.3995   $173.40   $173.40   $173.40  
  7 purchase totals = $1,108.14       $1,188.7287   $1,188.72   $1,188.75   $1,188.70