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	$116.72	9.476%	$127.7804	$127.78	$127.80	$127.80
Purchase #2	$79.57	4.482%	$83.1363	$83.14	$83.15	$83.10
Purchase #3	$62.60	8.294%	$67.792	$67.79	$67.80	$67.80
Purchase #4	$167.82	13.633%	$190.6989	$190.70	$190.70	$190.70
Purchase #5	$48.63	10.734%	$53.8499	$53.85	$53.85	$53.80
Purchase #6	$107.32	3.212%	$110.7671	$110.77	$110.75	$110.80
Purchase #7	$54.48	4.865%	$57.1305	$57.13	$57.15	$57.10
7 purchase totals =	$637.14		$691.1551	$691.16	$691.20	$691.10