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	$233.69	10.595%	$258.4495	$258.45	$258.45	$258.40
Purchase #2	$77.76	6.533%	$82.8401	$82.84	$82.85	$82.80
Purchase #3	$107.71	10.251%	$118.7514	$118.75	$118.75	$118.80
Purchase #4	$51.87	3.222%	$53.5413	$53.54	$53.55	$53.50
Purchase #5	$223.42	10.852%	$247.6655	$247.67	$247.65	$247.70
Purchase #6	$119.31	11.858%	$133.4578	$133.46	$133.45	$133.50
Purchase #7	$80.37	12.161%	$90.1438	$90.14	$90.15	$90.10
7 purchase totals =	$894.13		$984.8494	$984.85	$984.85	$984.80