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	$85.35	4.600%	$89.2761	$89.28	$89.30	$89.30
Purchase #2	$73.60	10.849%	$81.5849	$81.58	$81.60	$81.60
Purchase #3	$12.52	6.470%	$13.33	$13.33	$13.35	$13.30
Purchase #4	$18.49	5.863%	$19.5741	$19.57	$19.55	$19.60
Purchase #5	$132.57	7.486%	$142.4942	$142.49	$142.50	$142.50
Purchase #6	$64.98	10.277%	$71.658	$71.66	$71.65	$71.70
Purchase #7	$184.56	6.548%	$196.645	$196.65	$196.65	$196.60
7 purchase totals =	$572.07		$614.5623	$614.56	$614.60	$614.60