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	$45.31	10.146%	$49.9072	$49.91	$49.90	$49.90
Purchase #2	$49.49	11.274%	$55.0695	$55.07	$55.05	$55.10
Purchase #3	$57.28	7.452%	$61.5485	$61.55	$61.55	$61.50
Purchase #4	$226.31	5.580%	$238.9381	$238.94	$238.95	$238.90
Purchase #5	$104.37	6.436%	$111.0873	$111.09	$111.10	$111.10
Purchase #6	$228.31	3.277%	$235.7917	$235.79	$235.80	$235.80
Purchase #7	$34.45	4.650%	$36.0519	$36.05	$36.05	$36.10
7 purchase totals =	$745.52		$788.3942	$788.40	$788.40	$788.40