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	$18.93	13.410%	$21.4685	$21.47	$21.45	$21.50
Purchase #2	$236.73	11.640%	$264.2854	$264.29	$264.30	$264.30
Purchase #3	$48.89	13.766%	$55.6202	$55.62	$55.60	$55.60
Purchase #4	$140.68	3.674%	$145.8486	$145.85	$145.85	$145.80
Purchase #5	$105.63	5.622%	$111.5685	$111.57	$111.55	$111.60
Purchase #6	$229.37	5.117%	$241.1069	$241.11	$241.10	$241.10
Purchase #7	$174.29	7.786%	$187.8602	$187.86	$187.85	$187.90
7 purchase totals =	$954.52		$1,027.7583	$1,027.77	$1,027.70	$1,027.80