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	$92.76	11.356%	$103.2938	$103.29	$103.30	$103.30
Purchase #2	$73.43	7.212%	$78.7258	$78.73	$78.75	$78.70
Purchase #3	$153.93	12.823%	$173.6684	$173.67	$173.65	$173.70
Purchase #4	$18.40	10.649%	$20.3594	$20.36	$20.35	$20.40
Purchase #5	$25.85	8.418%	$28.0261	$28.03	$28.05	$28.00
Purchase #6	$147.68	7.602%	$158.9066	$158.91	$158.90	$158.90
Purchase #7	$35.45	10.123%	$39.0386	$39.04	$39.05	$39.00
7 purchase totals =	$547.50		$602.0187	$602.03	$602.05	$602.00