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	$81.80	12.650%	$92.1477	$92.15	$92.15	$92.10
Purchase #2	$159.49	8.354%	$172.8138	$172.81	$172.80	$172.80
Purchase #3	$154.30	11.764%	$172.4519	$172.45	$172.45	$172.50
Purchase #4	$32.51	10.245%	$35.8406	$35.84	$35.85	$35.80
Purchase #5	$216.64	13.363%	$245.5896	$245.59	$245.60	$245.60
Purchase #6	$108.60	9.674%	$119.106	$119.11	$119.10	$119.10
Purchase #7	$34.60	10.800%	$38.3368	$38.34	$38.35	$38.30
7 purchase totals =	$787.94		$876.2864	$876.29	$876.30	$876.20