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	$178.87	5.576%	$188.8438	$188.84	$188.85	$188.80
Purchase #2	$50.93	6.786%	$54.3861	$54.39	$54.40	$54.40
Purchase #3	$82.76	5.147%	$87.0197	$87.02	$87.00	$87.00
Purchase #4	$196.84	5.789%	$208.2351	$208.24	$208.25	$208.20
Purchase #5	$107.37	3.862%	$111.5166	$111.52	$111.50	$111.50
Purchase #6	$128.88	7.679%	$138.7767	$138.78	$138.80	$138.80
Purchase #7	$205.47	12.727%	$231.6202	$231.62	$231.60	$231.60
7 purchase totals =	$951.12		$1,020.3982	$1,020.41	$1,020.40	$1,020.30