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	$239.72	12.695%	$270.1525	$270.15	$270.15	$270.20
Purchase #2	$233.79	11.657%	$261.0429	$261.04	$261.05	$261.00
Purchase #3	$61.42	7.122%	$65.7943	$65.79	$65.80	$65.80
Purchase #4	$220.33	4.245%	$229.683	$229.68	$229.70	$229.70
Purchase #5	$150.31	6.199%	$159.6277	$159.63	$159.65	$159.60
Purchase #6	$70.91	10.845%	$78.6002	$78.60	$78.60	$78.60
Purchase #7	$11.92	4.729%	$12.4837	$12.48	$12.50	$12.50
7 purchase totals =	$988.40		$1,077.3843	$1,077.37	$1,077.45	$1,077.40