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	$61.58	7.367%	$66.1166	$66.12	$66.10	$66.10
Purchase #2	$72.82	12.621%	$82.0106	$82.01	$82.00	$82.00
Purchase #3	$97.68	13.151%	$110.5259	$110.53	$110.55	$110.50
Purchase #4	$240.47	6.110%	$255.1627	$255.16	$255.15	$255.20
Purchase #5	$94.32	5.471%	$99.4802	$99.48	$99.50	$99.50
Purchase #6	$207.71	11.171%	$230.9133	$230.91	$230.90	$230.90
Purchase #7	$89.45	11.176%	$99.4469	$99.45	$99.45	$99.40
7 purchase totals =	$864.03		$943.6562	$943.66	$943.65	$943.60