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	$111.86	10.417%	$123.5125	$123.51	$123.50	$123.50
Purchase #2	$70.75	6.319%	$75.2207	$75.22	$75.20	$75.20
Purchase #3	$172.45	10.586%	$190.7056	$190.71	$190.70	$190.70
Purchase #4	$14.92	3.656%	$15.4655	$15.47	$15.45	$15.50
Purchase #5	$48.53	3.276%	$50.1198	$50.12	$50.10	$50.10
Purchase #6	$54.95	7.769%	$59.2191	$59.22	$59.20	$59.20
Purchase #7	$87.68	13.190%	$99.245	$99.25	$99.25	$99.20
7 purchase totals =	$561.14		$613.4882	$613.50	$613.40	$613.40