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	$44.41	11.678%	$49.5962	$49.60	$49.60	$49.60
Purchase #2	$47.59	6.427%	$50.6486	$50.65	$50.65	$50.60
Purchase #3	$35.60	10.848%	$39.4619	$39.46	$39.45	$39.50
Purchase #4	$247.60	9.689%	$271.59	$271.59	$271.60	$271.60
Purchase #5	$51.91	4.316%	$54.1504	$54.15	$54.15	$54.20
Purchase #6	$31.49	6.600%	$33.5683	$33.57	$33.55	$33.60
Purchase #7	$55.66	7.297%	$59.7215	$59.72	$59.70	$59.70
7 purchase totals =	$514.26		$558.7369	$558.74	$558.70	$558.80