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 $115.81   3.319%   $119.6537   $119.65   $119.65   $119.70  
  Purchase #2 $194.26   3.138%   $200.3559   $200.36   $200.35   $200.40  
  Purchase #3 $64.55   3.404%   $66.7473   $66.75   $66.75   $66.70  
  Purchase #4 $234.86   11.461%   $261.7773   $261.78   $261.80   $261.80  
  Purchase #5 $72.55   7.437%   $77.9455   $77.95   $77.95   $77.90  
  Purchase #6 $241.98   7.292%   $259.6252   $259.63   $259.65   $259.60  
  Purchase #7 $196.76   8.843%   $214.1595   $214.16   $214.15   $214.20  
  7 purchase totals = $1,120.77       $1,200.2644   $1,200.28   $1,200.30   $1,200.30