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	$55.43	3.537%	$57.3906	$57.39	$57.40	$57.40
Purchase #2	$35.51	8.163%	$38.4087	$38.41	$38.40	$38.40
Purchase #3	$81.83	10.351%	$90.3002	$90.30	$90.30	$90.30
Purchase #4	$104.64	6.730%	$111.6823	$111.68	$111.70	$111.70
Purchase #5	$124.60	7.145%	$133.5027	$133.50	$133.50	$133.50
Purchase #6	$23.43	6.557%	$24.9663	$24.97	$24.95	$25.00
Purchase #7	$217.64	4.834%	$228.1607	$228.16	$228.15	$228.20
7 purchase totals =	$643.08		$684.4115	$684.41	$684.40	$684.50