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	$83.87	7.111%	$89.834	$89.83	$89.85	$89.80
Purchase #2	$22.53	4.536%	$23.552	$23.55	$23.55	$23.60
Purchase #3	$153.52	8.391%	$166.4019	$166.40	$166.40	$166.40
Purchase #4	$155.34	13.771%	$176.7319	$176.73	$176.75	$176.70
Purchase #5	$61.54	9.215%	$67.2109	$67.21	$67.20	$67.20
Purchase #6	$8.99	12.805%	$10.1412	$10.14	$10.15	$10.10
Purchase #7	$20.54	4.424%	$21.4487	$21.45	$21.45	$21.40
7 purchase totals =	$506.33		$555.3206	$555.31	$555.35	$555.20