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	$200.35	13.374%	$227.1448	$227.14	$227.15	$227.10
Purchase #2	$180.77	8.829%	$196.7302	$196.73	$196.75	$196.70
Purchase #3	$174.53	3.121%	$179.9771	$179.98	$180.00	$180.00
Purchase #4	$249.96	10.303%	$275.7134	$275.71	$275.70	$275.70
Purchase #5	$235.89	12.543%	$265.4777	$265.48	$265.50	$265.50
Purchase #6	$94.65	11.194%	$105.2451	$105.25	$105.25	$105.20
Purchase #7	$197.39	5.795%	$208.8288	$208.83	$208.85	$208.80
7 purchase totals =	$1,333.54		$1,459.1171	$1,459.12	$1,459.20	$1,459.00