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	$89.32	12.172%	$100.192	$100.19	$100.20	$100.20
Purchase #2	$240.60	6.539%	$256.3328	$256.33	$256.35	$256.30
Purchase #3	$137.40	8.516%	$149.101	$149.10	$149.10	$149.10
Purchase #4	$110.89	6.780%	$118.4083	$118.41	$118.40	$118.40
Purchase #5	$9.54	13.571%	$10.8347	$10.83	$10.85	$10.80
Purchase #6	$20.45	12.621%	$23.031	$23.03	$23.05	$23.00
Purchase #7	$151.64	13.749%	$172.489	$172.49	$172.50	$172.50
7 purchase totals =	$759.84		$830.3888	$830.38	$830.45	$830.30