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	$60.46	13.182%	$68.4298	$68.43	$68.45	$68.40
Purchase #2	$130.56	10.710%	$144.543	$144.54	$144.55	$144.50
Purchase #3	$172.51	5.647%	$182.2516	$182.25	$182.25	$182.30
Purchase #4	$121.73	4.590%	$127.3174	$127.32	$127.30	$127.30
Purchase #5	$61.49	9.285%	$67.1993	$67.20	$67.20	$67.20
Purchase #6	$244.85	3.804%	$254.1641	$254.16	$254.15	$254.20
Purchase #7	$204.30	8.469%	$221.6022	$221.60	$221.60	$221.60
7 purchase totals =	$995.90		$1,065.5074	$1,065.50	$1,065.50	$1,065.50