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	$146.45	4.815%	$153.5016	$153.50	$153.50	$153.50
Purchase #2	$173.77	5.535%	$183.3882	$183.39	$183.40	$183.40
Purchase #3	$223.49	11.303%	$248.7511	$248.75	$248.75	$248.80
Purchase #4	$77.71	5.288%	$81.8193	$81.82	$81.80	$81.80
Purchase #5	$100.28	10.763%	$111.0731	$111.07	$111.05	$111.10
Purchase #6	$70.25	7.659%	$75.6304	$75.63	$75.65	$75.60
Purchase #7	$59.32	13.113%	$67.0986	$67.10	$67.10	$67.10
7 purchase totals =	$851.27		$921.2623	$921.26	$921.25	$921.30