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	$237.71	13.646%	$270.1479	$270.15	$270.15	$270.10
Purchase #2	$184.29	3.501%	$190.742	$190.74	$190.75	$190.70
Purchase #3	$91.28	13.348%	$103.4641	$103.46	$103.45	$103.50
Purchase #4	$137.39	3.798%	$142.6081	$142.61	$142.60	$142.60
Purchase #5	$12.60	4.721%	$13.1948	$13.19	$13.20	$13.20
Purchase #6	$155.82	10.402%	$172.0284	$172.03	$172.05	$172.00
Purchase #7	$229.91	3.816%	$238.6834	$238.68	$238.70	$238.70
7 purchase totals =	$1,049.00		$1,130.8687	$1,130.86	$1,130.90	$1,130.80