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	$19.58	4.501%	$20.4613	$20.46	$20.45	$20.50
Purchase #2	$123.34	11.406%	$137.4082	$137.41	$137.40	$137.40
Purchase #3	$121.70	13.483%	$138.1088	$138.11	$138.10	$138.10
Purchase #4	$172.43	3.515%	$178.4909	$178.49	$178.50	$178.50
Purchase #5	$56.32	6.397%	$59.9228	$59.92	$59.90	$59.90
Purchase #6	$74.46	5.224%	$78.3498	$78.35	$78.35	$78.30
Purchase #7	$228.26	10.775%	$252.855	$252.86	$252.85	$252.90
7 purchase totals =	$796.09		$865.5968	$865.60	$865.55	$865.60