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	$152.56	4.408%	$159.2848	$159.28	$159.30	$159.30
Purchase #2	$118.57	8.408%	$128.5394	$128.54	$128.55	$128.50
Purchase #3	$167.86	3.353%	$173.4883	$173.49	$173.50	$173.50
Purchase #4	$82.39	13.211%	$93.2745	$93.27	$93.25	$93.30
Purchase #5	$95.50	5.376%	$100.6341	$100.63	$100.65	$100.60
Purchase #6	$111.64	7.348%	$119.8433	$119.84	$119.85	$119.80
Purchase #7	$191.34	13.469%	$217.1116	$217.11	$217.10	$217.10
7 purchase totals =	$919.86		$992.1760	$992.16	$992.20	$992.10