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	$109.64	7.874%	$118.2731	$118.27	$118.25	$118.30
Purchase #2	$116.88	5.188%	$122.9437	$122.94	$122.95	$122.90
Purchase #3	$141.72	10.364%	$156.4079	$156.41	$156.40	$156.40
Purchase #4	$39.90	6.671%	$42.5617	$42.56	$42.55	$42.60
Purchase #5	$129.89	10.444%	$143.4557	$143.46	$143.45	$143.50
Purchase #6	$103.28	9.538%	$113.1308	$113.13	$113.15	$113.10
Purchase #7	$235.28	13.422%	$266.8593	$266.86	$266.85	$266.90
7 purchase totals =	$876.59		$963.6322	$963.63	$963.60	$963.70