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	$250.46	11.225%	$278.5741	$278.57	$278.55	$278.60
Purchase #2	$151.59	5.139%	$159.3802	$159.38	$159.40	$159.40
Purchase #3	$16.42	12.421%	$18.4595	$18.46	$18.45	$18.50
Purchase #4	$9.60	12.218%	$10.7729	$10.77	$10.75	$10.80
Purchase #5	$127.62	12.697%	$143.8239	$143.82	$143.80	$143.80
Purchase #6	$212.77	13.203%	$240.862	$240.86	$240.85	$240.90
Purchase #7	$52.25	12.787%	$58.9312	$58.93	$58.95	$58.90
7 purchase totals =	$820.71		$910.8038	$910.79	$910.75	$910.90