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	$235.55	3.495%	$243.7825	$243.78	$243.80	$243.80
Purchase #2	$10.87	10.254%	$11.9846	$11.98	$12.00	$12.00
Purchase #3	$197.56	12.795%	$222.8378	$222.84	$222.85	$222.80
Purchase #4	$126.97	9.721%	$139.3128	$139.31	$139.30	$139.30
Purchase #5	$200.26	9.672%	$219.6291	$219.63	$219.65	$219.60
Purchase #6	$56.96	4.406%	$59.4697	$59.47	$59.45	$59.50
Purchase #7	$174.64	12.468%	$196.4141	$196.41	$196.40	$196.40
7 purchase totals =	$1,002.81		$1,093.4306	$1,093.42	$1,093.45	$1,093.40