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	$159.81	3.440%	$165.3075	$165.31	$165.30	$165.30
Purchase #2	$78.77	12.122%	$88.3185	$88.32	$88.30	$88.30
Purchase #3	$71.82	11.162%	$79.8365	$79.84	$79.85	$79.80
Purchase #4	$222.80	3.414%	$230.4064	$230.41	$230.40	$230.40
Purchase #5	$70.66	10.792%	$78.2856	$78.29	$78.30	$78.30
Purchase #6	$179.44	11.487%	$200.0523	$200.05	$200.05	$200.10
Purchase #7	$19.91	12.789%	$22.4563	$22.46	$22.45	$22.50
7 purchase totals =	$803.21		$864.6631	$864.68	$864.65	$864.70