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	$39.65	9.754%	$43.5175	$43.52	$43.50	$43.50
Purchase #2	$109.77	12.102%	$123.0544	$123.05	$123.05	$123.10
Purchase #3	$210.74	6.382%	$224.1894	$224.19	$224.20	$224.20
Purchase #4	$237.65	10.444%	$262.4702	$262.47	$262.45	$262.50
Purchase #5	$161.43	3.111%	$166.4521	$166.45	$166.45	$166.50
Purchase #6	$90.28	9.170%	$98.5587	$98.56	$98.55	$98.60
Purchase #7	$229.58	10.544%	$253.7869	$253.79	$253.80	$253.80
7 purchase totals =	$1,079.10		$1,172.0292	$1,172.03	$1,172.00	$1,172.20