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	$90.92	10.461%	$100.4311	$100.43	$100.45	$100.40
Purchase #2	$225.57	5.715%	$238.4613	$238.46	$238.45	$238.50
Purchase #3	$222.69	6.710%	$237.6325	$237.63	$237.65	$237.60
Purchase #4	$132.86	10.122%	$146.3081	$146.31	$146.30	$146.30
Purchase #5	$11.72	6.721%	$12.5077	$12.51	$12.50	$12.50
Purchase #6	$114.51	13.644%	$130.1337	$130.13	$130.15	$130.10
Purchase #7	$20.64	13.502%	$23.4268	$23.43	$23.45	$23.40
7 purchase totals =	$818.91		$888.9012	$888.90	$888.95	$888.80