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	$230.72	3.135%	$237.9531	$237.95	$237.95	$238.00
Purchase #2	$32.69	7.333%	$35.0872	$35.09	$35.10	$35.10
Purchase #3	$243.69	4.567%	$254.8193	$254.82	$254.80	$254.80
Purchase #4	$139.85	10.536%	$154.5846	$154.58	$154.60	$154.60
Purchase #5	$157.85	9.505%	$172.8536	$172.85	$172.85	$172.90
Purchase #6	$53.34	11.448%	$59.4464	$59.45	$59.45	$59.40
Purchase #7	$162.80	8.128%	$176.0324	$176.03	$176.05	$176.00
7 purchase totals =	$1,020.94		$1,090.7766	$1,090.77	$1,090.80	$1,090.80