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	$75.43	4.202%	$78.5996	$78.60	$78.60	$78.60
Purchase #2	$99.75	9.505%	$109.2312	$109.23	$109.25	$109.20
Purchase #3	$151.75	10.162%	$167.1708	$167.17	$167.15	$167.20
Purchase #4	$235.33	10.676%	$260.4538	$260.45	$260.45	$260.50
Purchase #5	$21.78	10.766%	$24.1248	$24.12	$24.10	$24.10
Purchase #6	$88.91	5.524%	$93.8214	$93.82	$93.80	$93.80
Purchase #7	$71.72	3.554%	$74.2689	$74.27	$74.25	$74.30
7 purchase totals =	$744.67		$807.6705	$807.66	$807.60	$807.70