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	$90.57	10.501%	$100.0808	$100.08	$100.10	$100.10
Purchase #2	$62.41	7.766%	$67.2568	$67.26	$67.25	$67.30
Purchase #3	$195.54	7.515%	$210.2348	$210.23	$210.25	$210.20
Purchase #4	$158.31	10.398%	$174.7711	$174.77	$174.75	$174.80
Purchase #5	$184.35	3.388%	$190.5958	$190.60	$190.60	$190.60
Purchase #6	$238.51	8.657%	$259.1578	$259.16	$259.15	$259.20
Purchase #7	$143.61	9.824%	$157.7182	$157.72	$157.70	$157.70
7 purchase totals =	$1,073.30		$1,159.8153	$1,159.82	$1,159.80	$1,159.90