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	$226.32	10.480%	$250.0383	$250.04	$250.05	$250.00
Purchase #2	$185.49	4.213%	$193.3047	$193.30	$193.30	$193.30
Purchase #3	$138.27	3.761%	$143.4703	$143.47	$143.45	$143.50
Purchase #4	$45.25	11.367%	$50.3936	$50.39	$50.40	$50.40
Purchase #5	$241.40	6.217%	$256.4078	$256.41	$256.40	$256.40
Purchase #6	$240.72	5.477%	$253.9042	$253.90	$253.90	$253.90
Purchase #7	$16.92	6.836%	$18.0767	$18.08	$18.10	$18.10
7 purchase totals =	$1,094.37		$1,165.5956	$1,165.59	$1,165.60	$1,165.60