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	$85.60	4.342%	$89.3168	$89.32	$89.30	$89.30
Purchase #2	$204.44	13.117%	$231.2564	$231.26	$231.25	$231.30
Purchase #3	$123.69	12.383%	$139.0065	$139.01	$139.00	$139.00
Purchase #4	$161.26	6.346%	$171.4936	$171.49	$171.50	$171.50
Purchase #5	$56.85	10.264%	$62.6851	$62.69	$62.70	$62.70
Purchase #6	$230.29	4.800%	$241.3439	$241.34	$241.35	$241.30
Purchase #7	$26.95	12.764%	$30.3899	$30.39	$30.40	$30.40
7 purchase totals =	$889.08		$965.4922	$965.50	$965.50	$965.50