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	$172.56	10.287%	$190.3112	$190.31	$190.30	$190.30
Purchase #2	$21.60	4.201%	$22.5074	$22.51	$22.50	$22.50
Purchase #3	$144.71	9.439%	$158.3692	$158.37	$158.35	$158.40
Purchase #4	$79.83	10.267%	$88.0261	$88.03	$88.05	$88.00
Purchase #5	$103.88	10.624%	$114.9162	$114.92	$114.90	$114.90
Purchase #6	$96.27	6.351%	$102.3841	$102.38	$102.40	$102.40
Purchase #7	$62.99	7.794%	$67.8994	$67.90	$67.90	$67.90
7 purchase totals =	$681.84		$744.4136	$744.42	$744.40	$744.40