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	$97.49	9.364%	$106.619	$106.62	$106.60	$106.60
Purchase #2	$211.70	12.785%	$238.7658	$238.77	$238.75	$238.80
Purchase #3	$49.77	12.195%	$55.8395	$55.84	$55.85	$55.80
Purchase #4	$71.62	6.704%	$76.4214	$76.42	$76.40	$76.40
Purchase #5	$42.89	6.821%	$45.8155	$45.82	$45.80	$45.80
Purchase #6	$51.31	4.134%	$53.4312	$53.43	$53.45	$53.40
Purchase #7	$160.61	9.131%	$175.2753	$175.28	$175.30	$175.30
7 purchase totals =	$685.39		$752.1677	$752.18	$752.15	$752.10