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	$49.34	7.240%	$52.9122	$52.91	$52.90	$52.90
Purchase #2	$85.89	4.690%	$89.9182	$89.92	$89.90	$89.90
Purchase #3	$118.35	12.191%	$132.778	$132.78	$132.80	$132.80
Purchase #4	$66.27	3.323%	$68.4722	$68.47	$68.45	$68.50
Purchase #5	$192.68	6.728%	$205.6435	$205.64	$205.65	$205.60
Purchase #6	$208.59	10.727%	$230.9654	$230.97	$230.95	$231.00
Purchase #7	$190.35	3.350%	$196.7267	$196.73	$196.75	$196.70
7 purchase totals =	$911.47		$977.4162	$977.42	$977.40	$977.40