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	$19.69	4.842%	$20.6434	$20.64	$20.65	$20.60
Purchase #2	$238.45	6.796%	$254.6551	$254.66	$254.65	$254.70
Purchase #3	$184.37	13.673%	$209.5789	$209.58	$209.60	$209.60
Purchase #4	$98.35	5.873%	$104.1261	$104.13	$104.15	$104.10
Purchase #5	$63.92	4.469%	$66.7766	$66.78	$66.80	$66.80
Purchase #6	$134.98	11.346%	$150.2948	$150.29	$150.30	$150.30
Purchase #7	$98.53	13.588%	$111.9183	$111.92	$111.90	$111.90
7 purchase totals =	$838.29		$917.9932	$918.00	$918.05	$918.00