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 $242.99   10.587%   $268.7154   $268.72   $268.70   $268.70  
  Purchase #2 $211.28   7.770%   $227.6965   $227.70   $227.70   $227.70  
  Purchase #3 $45.64   6.261%   $48.4975   $48.50   $48.50   $48.50  
  Purchase #4 $34.81   10.282%   $38.3892   $38.39   $38.40   $38.40  
  Purchase #5 $211.50   10.632%   $233.9867   $233.99   $234.00   $234.00  
  Purchase #6 $51.53   3.622%   $53.3964   $53.40   $53.40   $53.40  
  Purchase #7 $229.69   9.235%   $250.9019   $250.90   $250.90   $250.90  
  7 purchase totals = $1,027.44       $1,121.5836   $1,121.60   $1,121.60   $1,121.60