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	$127.32	9.451%	$139.353	$139.35	$139.35	$139.40
Purchase #2	$111.87	12.777%	$126.1636	$126.16	$126.15	$126.20
Purchase #3	$117.99	9.235%	$128.8864	$128.89	$128.90	$128.90
Purchase #4	$39.95	4.767%	$41.8544	$41.85	$41.85	$41.90
Purchase #5	$152.73	13.125%	$172.7758	$172.78	$172.80	$172.80
Purchase #6	$167.65	4.695%	$175.5212	$175.52	$175.50	$175.50
Purchase #7	$173.35	9.159%	$189.2271	$189.23	$189.25	$189.20
7 purchase totals =	$890.86		$973.7815	$973.78	$973.80	$973.90