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	$37.44	13.455%	$42.4776	$42.48	$42.50	$42.50
Purchase #2	$91.70	9.602%	$100.505	$100.51	$100.50	$100.50
Purchase #3	$70.99	10.542%	$78.4738	$78.47	$78.45	$78.50
Purchase #4	$113.26	13.557%	$128.6147	$128.61	$128.60	$128.60
Purchase #5	$7.46	3.134%	$7.6938	$7.69	$7.70	$7.70
Purchase #6	$18.40	3.176%	$18.9844	$18.98	$19.00	$19.00
Purchase #7	$62.43	3.709%	$64.7455	$64.75	$64.75	$64.70
7 purchase totals =	$401.68		$441.4948	$441.49	$441.50	$441.50