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	$88.43	13.762%	$100.5997	$100.60	$100.60	$100.60
Purchase #2	$158.97	5.500%	$167.7134	$167.71	$167.70	$167.70
Purchase #3	$121.83	10.306%	$134.3858	$134.39	$134.40	$134.40
Purchase #4	$66.87	6.611%	$71.2908	$71.29	$71.30	$71.30
Purchase #5	$30.71	13.700%	$34.9173	$34.92	$34.90	$34.90
Purchase #6	$142.31	12.121%	$159.5594	$159.56	$159.55	$159.60
Purchase #7	$64.46	10.257%	$71.0717	$71.07	$71.05	$71.10
7 purchase totals =	$673.58		$739.5381	$739.54	$739.50	$739.60