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	$10.57	13.335%	$11.9795	$11.98	$12.00	$12.00
Purchase #2	$204.46	5.502%	$215.7094	$215.71	$215.70	$215.70
Purchase #3	$40.36	13.389%	$45.7638	$45.76	$45.75	$45.80
Purchase #4	$50.44	7.244%	$54.0939	$54.09	$54.10	$54.10
Purchase #5	$215.46	7.161%	$230.8891	$230.89	$230.90	$230.90
Purchase #6	$134.65	9.206%	$147.0459	$147.05	$147.05	$147.00
Purchase #7	$54.34	8.686%	$59.06	$59.06	$59.05	$59.10
7 purchase totals =	$710.28		$764.5416	$764.54	$764.55	$764.60