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	$37.95	6.826%	$40.5405	$40.54	$40.55	$40.50
Purchase #2	$214.35	10.662%	$237.204	$237.20	$237.20	$237.20
Purchase #3	$12.83	10.358%	$14.1589	$14.16	$14.15	$14.20
Purchase #4	$53.58	4.194%	$55.8271	$55.83	$55.85	$55.80
Purchase #5	$56.97	5.712%	$60.2241	$60.22	$60.20	$60.20
Purchase #6	$12.91	4.387%	$13.4764	$13.48	$13.50	$13.50
Purchase #7	$173.25	13.291%	$196.2767	$196.28	$196.30	$196.30
7 purchase totals =	$561.84		$617.7077	$617.71	$617.75	$617.70