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 $228.63   7.807%   $246.4791   $246.48   $246.50   $246.50  
  Purchase #2 $224.35   11.183%   $249.4391   $249.44   $249.45   $249.40  
  Purchase #3 $222.61   6.763%   $237.6651   $237.67   $237.65   $237.70  
  Purchase #4 $91.44   7.346%   $98.1572   $98.16   $98.15   $98.20  
  Purchase #5 $221.91   6.609%   $236.576   $236.58   $236.60   $236.60  
  Purchase #6 $115.36   10.687%   $127.6885   $127.69   $127.70   $127.70  
  Purchase #7 $43.48   11.116%   $48.3132   $48.31   $48.30   $48.30  
  7 purchase totals = $1,147.78       $1,244.3182   $1,244.33   $1,244.35   $1,244.40