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	$61.77	5.126%	$64.9363	$64.94	$64.95	$64.90
Purchase #2	$241.35	10.839%	$267.5099	$267.51	$267.50	$267.50
Purchase #3	$241.85	9.758%	$265.4497	$265.45	$265.45	$265.40
Purchase #4	$205.41	7.603%	$221.0273	$221.03	$221.05	$221.00
Purchase #5	$152.46	13.124%	$172.4689	$172.47	$172.45	$172.50
Purchase #6	$143.58	8.845%	$156.2797	$156.28	$156.30	$156.30
Purchase #7	$161.56	6.823%	$172.5832	$172.58	$172.60	$172.60
7 purchase totals =	$1,207.98		$1,320.2550	$1,320.26	$1,320.30	$1,320.20