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	$34.89	11.489%	$38.8985	$38.90	$38.90	$38.90
Purchase #2	$208.65	4.778%	$218.6193	$218.62	$218.60	$218.60
Purchase #3	$112.47	13.512%	$127.6669	$127.67	$127.65	$127.70
Purchase #4	$153.42	7.741%	$165.2962	$165.30	$165.30	$165.30
Purchase #5	$218.61	6.821%	$233.5214	$233.52	$233.50	$233.50
Purchase #6	$90.25	13.774%	$102.681	$102.68	$102.70	$102.70
Purchase #7	$214.33	3.763%	$222.3952	$222.40	$222.40	$222.40
7 purchase totals =	$1,032.62		$1,109.0785	$1,109.09	$1,109.05	$1,109.10