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	$8.89	13.635%	$10.1022	$10.10	$10.10	$10.10
Purchase #2	$148.84	3.227%	$153.6431	$153.64	$153.65	$153.60
Purchase #3	$98.83	4.173%	$102.9542	$102.95	$102.95	$103.00
Purchase #4	$33.60	3.692%	$34.8405	$34.84	$34.85	$34.80
Purchase #5	$78.91	4.246%	$82.2605	$82.26	$82.25	$82.30
Purchase #6	$58.71	10.439%	$64.8387	$64.84	$64.85	$64.80
Purchase #7	$196.80	10.526%	$217.5152	$217.52	$217.50	$217.50
7 purchase totals =	$624.58		$666.1544	$666.15	$666.15	$666.10