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	$107.52	3.394%	$111.1692	$111.17	$111.15	$111.20
Purchase #2	$125.50	7.479%	$134.8861	$134.89	$134.90	$134.90
Purchase #3	$13.87	10.319%	$15.3012	$15.30	$15.30	$15.30
Purchase #4	$78.82	13.406%	$89.3866	$89.39	$89.40	$89.40
Purchase #5	$162.49	8.414%	$176.1619	$176.16	$176.15	$176.20
Purchase #6	$45.33	9.781%	$49.7637	$49.76	$49.75	$49.80
Purchase #7	$230.51	13.840%	$262.4126	$262.41	$262.40	$262.40
7 purchase totals =	$764.04		$839.0813	$839.08	$839.05	$839.20