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	$36.32	10.613%	$40.1746	$40.17	$40.15	$40.20
Purchase #2	$153.75	13.361%	$174.2925	$174.29	$174.30	$174.30
Purchase #3	$26.38	3.538%	$27.3133	$27.31	$27.30	$27.30
Purchase #4	$226.75	6.867%	$242.3209	$242.32	$242.30	$242.30
Purchase #5	$48.77	12.575%	$54.9028	$54.90	$54.90	$54.90
Purchase #6	$244.91	9.761%	$268.8157	$268.82	$268.80	$268.80
Purchase #7	$118.81	13.149%	$134.4323	$134.43	$134.45	$134.40
7 purchase totals =	$855.69		$942.2521	$942.24	$942.20	$942.20