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	$129.32	10.789%	$143.2723	$143.27	$143.25	$143.30
Purchase #2	$64.71	13.168%	$73.231	$73.23	$73.25	$73.20
Purchase #3	$103.89	4.641%	$108.7115	$108.71	$108.70	$108.70
Purchase #4	$72.67	8.590%	$78.9124	$78.91	$78.90	$78.90
Purchase #5	$249.53	9.245%	$272.599	$272.60	$272.60	$272.60
Purchase #6	$49.90	8.463%	$54.123	$54.12	$54.10	$54.10
Purchase #7	$216.50	9.560%	$237.1974	$237.20	$237.20	$237.20
7 purchase totals =	$886.52		$968.0466	$968.04	$968.00	$968.00