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	$179.27	8.457%	$194.4309	$194.43	$194.45	$194.40
Purchase #2	$36.52	13.536%	$41.4633	$41.46	$41.45	$41.50
Purchase #3	$98.78	13.283%	$111.9009	$111.90	$111.90	$111.90
Purchase #4	$241.44	7.711%	$260.0574	$260.06	$260.05	$260.10
Purchase #5	$171.27	11.473%	$190.9198	$190.92	$190.90	$190.90
Purchase #6	$102.44	10.710%	$113.4113	$113.41	$113.40	$113.40
Purchase #7	$14.68	7.415%	$15.7685	$15.77	$15.75	$15.80
7 purchase totals =	$844.40		$927.9521	$927.95	$927.90	$928.00