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	$184.32	8.448%	$199.8914	$199.89	$199.90	$199.90
Purchase #2	$215.78	10.711%	$238.8922	$238.89	$238.90	$238.90
Purchase #3	$83.76	7.628%	$90.1492	$90.15	$90.15	$90.10
Purchase #4	$26.44	11.631%	$29.5152	$29.52	$29.50	$29.50
Purchase #5	$89.60	12.795%	$101.0643	$101.06	$101.05	$101.10
Purchase #6	$57.95	13.410%	$65.7211	$65.72	$65.70	$65.70
Purchase #7	$169.84	9.335%	$185.6946	$185.69	$185.70	$185.70
7 purchase totals =	$827.69		$910.9280	$910.92	$910.90	$910.90