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	$243.96	13.468%	$276.8165	$276.82	$276.80	$276.80
Purchase #2	$99.97	11.211%	$111.1776	$111.18	$111.20	$111.20
Purchase #3	$89.57	5.865%	$94.8233	$94.82	$94.80	$94.80
Purchase #4	$134.73	13.389%	$152.769	$152.77	$152.75	$152.80
Purchase #5	$165.39	12.849%	$186.641	$186.64	$186.65	$186.60
Purchase #6	$137.70	10.808%	$152.5826	$152.58	$152.60	$152.60
Purchase #7	$122.63	3.777%	$127.2617	$127.26	$127.25	$127.30
7 purchase totals =	$993.95		$1,102.0717	$1,102.07	$1,102.05	$1,102.10