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	$70.59	12.207%	$79.2069	$79.21	$79.20	$79.20
Purchase #2	$18.43	7.707%	$19.8504	$19.85	$19.85	$19.90
Purchase #3	$176.69	5.866%	$187.0546	$187.05	$187.05	$187.10
Purchase #4	$76.31	9.170%	$83.3076	$83.31	$83.30	$83.30
Purchase #5	$18.47	9.851%	$20.2895	$20.29	$20.30	$20.30
Purchase #6	$235.56	8.569%	$255.7451	$255.75	$255.75	$255.70
Purchase #7	$86.85	3.162%	$89.5962	$89.60	$89.60	$89.60
7 purchase totals =	$682.90		$735.0503	$735.06	$735.05	$735.10