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	$205.35	12.449%	$230.914	$230.91	$230.90	$230.90
Purchase #2	$49.81	10.342%	$54.9614	$54.96	$54.95	$55.00
Purchase #3	$166.68	11.178%	$185.3115	$185.31	$185.30	$185.30
Purchase #4	$52.26	9.554%	$57.2529	$57.25	$57.25	$57.30
Purchase #5	$61.98	5.470%	$65.3703	$65.37	$65.35	$65.40
Purchase #6	$61.38	4.595%	$64.2004	$64.20	$64.20	$64.20
Purchase #7	$181.68	4.808%	$190.4152	$190.42	$190.40	$190.40
7 purchase totals =	$779.14		$848.4257	$848.42	$848.35	$848.50