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	$44.51	13.401%	$50.4748	$50.47	$50.45	$50.50
Purchase #2	$248.55	8.142%	$268.7869	$268.79	$268.80	$268.80
Purchase #3	$52.76	3.827%	$54.7791	$54.78	$54.80	$54.80
Purchase #4	$225.94	10.817%	$250.3799	$250.38	$250.40	$250.40
Purchase #5	$157.73	5.365%	$166.1922	$166.19	$166.20	$166.20
Purchase #6	$179.70	10.277%	$198.1678	$198.17	$198.15	$198.20
Purchase #7	$146.79	4.632%	$153.5893	$153.59	$153.60	$153.60
7 purchase totals =	$1,055.98		$1,142.3700	$1,142.37	$1,142.40	$1,142.50