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	$62.73	7.308%	$67.3143	$67.31	$67.30	$67.30
Purchase #2	$228.60	11.371%	$254.5941	$254.59	$254.60	$254.60
Purchase #3	$119.60	6.794%	$127.7256	$127.73	$127.75	$127.70
Purchase #4	$225.57	7.477%	$242.4359	$242.44	$242.45	$242.40
Purchase #5	$81.75	4.238%	$85.2146	$85.21	$85.20	$85.20
Purchase #6	$200.30	12.246%	$224.8287	$224.83	$224.85	$224.80
Purchase #7	$167.79	13.239%	$190.0037	$190.00	$190.00	$190.00
7 purchase totals =	$1,086.34		$1,192.1169	$1,192.11	$1,192.15	$1,192.00