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	$123.39	11.210%	$137.222	$137.22	$137.20	$137.20
Purchase #2	$123.56	10.652%	$136.7216	$136.72	$136.70	$136.70
Purchase #3	$166.50	5.733%	$176.0454	$176.05	$176.05	$176.00
Purchase #4	$77.89	10.601%	$86.1471	$86.15	$86.15	$86.10
Purchase #5	$237.87	5.134%	$250.0822	$250.08	$250.10	$250.10
Purchase #6	$105.68	6.764%	$112.8282	$112.83	$112.85	$112.80
Purchase #7	$217.42	3.633%	$225.3189	$225.32	$225.30	$225.30
7 purchase totals =	$1,052.31		$1,124.3654	$1,124.37	$1,124.35	$1,124.20