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	$225.94	12.560%	$254.3181	$254.32	$254.30	$254.30
Purchase #2	$149.39	6.111%	$158.5192	$158.52	$158.50	$158.50
Purchase #3	$165.79	7.393%	$178.0469	$178.05	$178.05	$178.00
Purchase #4	$11.40	13.460%	$12.9344	$12.93	$12.95	$12.90
Purchase #5	$143.42	6.453%	$152.6749	$152.67	$152.65	$152.70
Purchase #6	$166.59	12.379%	$187.2122	$187.21	$187.20	$187.20
Purchase #7	$246.77	13.437%	$279.9285	$279.93	$279.95	$279.90
7 purchase totals =	$1,109.30		$1,223.6342	$1,223.63	$1,223.60	$1,223.50