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	$111.64	6.510%	$118.9078	$118.91	$118.90	$118.90
Purchase #2	$169.99	7.373%	$182.5234	$182.52	$182.50	$182.50
Purchase #3	$216.58	11.852%	$242.2491	$242.25	$242.25	$242.20
Purchase #4	$127.42	3.800%	$132.262	$132.26	$132.25	$132.30
Purchase #5	$35.37	13.305%	$40.076	$40.08	$40.10	$40.10
Purchase #6	$62.49	7.321%	$67.0649	$67.06	$67.05	$67.10
Purchase #7	$227.78	3.516%	$235.7887	$235.79	$235.80	$235.80
7 purchase totals =	$951.27		$1,018.8719	$1,018.87	$1,018.85	$1,018.90