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	$236.45	4.629%	$247.3953	$247.40	$247.40	$247.40
Purchase #2	$233.45	7.322%	$250.5432	$250.54	$250.55	$250.50
Purchase #3	$37.95	12.203%	$42.581	$42.58	$42.60	$42.60
Purchase #4	$128.29	9.453%	$140.4173	$140.42	$140.40	$140.40
Purchase #5	$64.71	13.605%	$73.5138	$73.51	$73.50	$73.50
Purchase #6	$155.43	11.826%	$173.8112	$173.81	$173.80	$173.80
Purchase #7	$84.83	6.502%	$90.3456	$90.35	$90.35	$90.30
7 purchase totals =	$941.11		$1,018.6074	$1,018.61	$1,018.60	$1,018.50