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	$48.54	13.198%	$54.9463	$54.95	$54.95	$54.90
Purchase #2	$97.42	13.493%	$110.5649	$110.56	$110.55	$110.60
Purchase #3	$224.69	11.504%	$250.5383	$250.54	$250.55	$250.50
Purchase #4	$215.74	3.605%	$223.5174	$223.52	$223.50	$223.50
Purchase #5	$140.65	7.753%	$151.5546	$151.55	$151.55	$151.60
Purchase #6	$159.89	4.762%	$167.504	$167.50	$167.50	$167.50
Purchase #7	$122.88	12.739%	$138.5337	$138.53	$138.55	$138.50
7 purchase totals =	$1,009.81		$1,097.1592	$1,097.15	$1,097.15	$1,097.10