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	$81.85	9.351%	$89.5038	$89.50	$89.50	$89.50
Purchase #2	$187.69	6.610%	$200.0963	$200.10	$200.10	$200.10
Purchase #3	$11.37	13.634%	$12.9202	$12.92	$12.90	$12.90
Purchase #4	$92.60	11.732%	$103.4638	$103.46	$103.45	$103.50
Purchase #5	$32.92	7.363%	$35.3439	$35.34	$35.35	$35.30
Purchase #6	$14.34	12.526%	$16.1362	$16.14	$16.15	$16.10
Purchase #7	$64.40	13.678%	$73.2086	$73.21	$73.20	$73.20
7 purchase totals =	$485.17		$530.6728	$530.67	$530.65	$530.60