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	$134.79	3.809%	$139.9242	$139.92	$139.90	$139.90
Purchase #2	$25.48	3.362%	$26.3366	$26.34	$26.35	$26.30
Purchase #3	$13.69	13.839%	$15.5846	$15.58	$15.60	$15.60
Purchase #4	$139.51	7.852%	$150.4643	$150.46	$150.45	$150.50
Purchase #5	$47.75	12.777%	$53.851	$53.85	$53.85	$53.90
Purchase #6	$97.57	13.792%	$111.0269	$111.03	$111.05	$111.00
Purchase #7	$94.26	3.247%	$97.3206	$97.32	$97.30	$97.30
7 purchase totals =	$553.05		$594.5082	$594.50	$594.50	$594.50