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 $242.64   8.291%   $262.7573   $262.76   $262.75   $262.80  
  Purchase #2 $100.63   10.658%   $111.3551   $111.36   $111.35   $111.40  
  Purchase #3 $114.89   4.480%   $120.0371   $120.04   $120.05   $120.00  
  Purchase #4 $214.29   11.751%   $239.4712   $239.47   $239.45   $239.50  
  Purchase #5 $227.95   7.295%   $244.579   $244.58   $244.60   $244.60  
  Purchase #6 $24.36   13.246%   $27.5867   $27.59   $27.60   $27.60  
  Purchase #7 $222.92   10.618%   $246.5896   $246.59   $246.60   $246.60  
  7 purchase totals = $1,147.68       $1,252.3760   $1,252.39   $1,252.40   $1,252.50