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	$33.72	5.353%	$35.525	$35.53	$35.55	$35.50
Purchase #2	$203.54	13.190%	$230.3869	$230.39	$230.40	$230.40
Purchase #3	$6.81	10.439%	$7.5209	$7.52	$7.50	$7.50
Purchase #4	$234.40	7.370%	$251.6753	$251.68	$251.70	$251.70
Purchase #5	$32.86	13.795%	$37.393	$37.39	$37.40	$37.40
Purchase #6	$16.37	7.421%	$17.5848	$17.58	$17.60	$17.60
Purchase #7	$53.92	10.711%	$59.6954	$59.70	$59.70	$59.70
7 purchase totals =	$581.62		$639.7813	$639.79	$639.85	$639.80