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	$248.39	9.613%	$272.2677	$272.27	$272.25	$272.30
Purchase #2	$112.74	9.491%	$123.4402	$123.44	$123.45	$123.40
Purchase #3	$240.31	9.225%	$262.4786	$262.48	$262.50	$262.50
Purchase #4	$98.92	9.684%	$108.4994	$108.50	$108.50	$108.50
Purchase #5	$143.71	5.534%	$151.6629	$151.66	$151.65	$151.70
Purchase #6	$65.75	9.113%	$71.7418	$71.74	$71.75	$71.70
Purchase #7	$16.97	9.650%	$18.6076	$18.61	$18.60	$18.60
7 purchase totals =	$926.79		$1,008.6982	$1,008.70	$1,008.70	$1,008.70