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	$99.81	5.690%	$105.4892	$105.49	$105.50	$105.50
Purchase #2	$80.68	10.719%	$89.3281	$89.33	$89.35	$89.30
Purchase #3	$112.66	12.803%	$127.0839	$127.08	$127.10	$127.10
Purchase #4	$42.40	10.380%	$46.8011	$46.80	$46.80	$46.80
Purchase #5	$14.27	6.475%	$15.194	$15.19	$15.20	$15.20
Purchase #6	$165.97	4.686%	$173.7474	$173.75	$173.75	$173.70
Purchase #7	$51.70	7.392%	$55.5217	$55.52	$55.50	$55.50
7 purchase totals =	$567.49		$613.1654	$613.16	$613.20	$613.10