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	$29.60	11.501%	$33.0043	$33.00	$33.00	$33.00
Purchase #2	$119.62	9.330%	$130.7805	$130.78	$130.80	$130.80
Purchase #3	$113.50	12.204%	$127.3515	$127.35	$127.35	$127.40
Purchase #4	$87.88	13.341%	$99.6041	$99.60	$99.60	$99.60
Purchase #5	$73.82	8.861%	$80.3612	$80.36	$80.35	$80.40
Purchase #6	$64.39	3.403%	$66.5812	$66.58	$66.60	$66.60
Purchase #7	$63.59	10.296%	$70.1372	$70.14	$70.15	$70.10
7 purchase totals =	$552.40		$607.8200	$607.81	$607.85	$607.90