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	$50.55	10.297%	$55.7551	$55.76	$55.75	$55.80
Purchase #2	$130.92	13.183%	$148.1792	$148.18	$148.20	$148.20
Purchase #3	$56.60	9.810%	$62.1525	$62.15	$62.15	$62.20
Purchase #4	$187.72	4.685%	$196.5147	$196.51	$196.50	$196.50
Purchase #5	$63.61	4.707%	$66.6041	$66.60	$66.60	$66.60
Purchase #6	$172.58	13.862%	$196.503	$196.50	$196.50	$196.50
Purchase #7	$226.27	12.532%	$254.6262	$254.63	$254.65	$254.60
7 purchase totals =	$888.25		$980.3348	$980.33	$980.35	$980.40