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	$155.94	11.522%	$173.9074	$173.91	$173.90	$173.90
Purchase #2	$116.36	13.360%	$131.9057	$131.91	$131.90	$131.90
Purchase #3	$128.73	8.209%	$139.2974	$139.30	$139.30	$139.30
Purchase #4	$222.50	8.115%	$240.5559	$240.56	$240.55	$240.60
Purchase #5	$153.36	12.722%	$172.8705	$172.87	$172.85	$172.90
Purchase #6	$138.37	9.210%	$151.1139	$151.11	$151.10	$151.10
Purchase #7	$80.30	6.432%	$85.4649	$85.46	$85.45	$85.50
7 purchase totals =	$995.56		$1,095.1157	$1,095.12	$1,095.05	$1,095.20