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	$81.29	10.355%	$89.7076	$89.71	$89.70	$89.70
Purchase #2	$167.53	3.691%	$173.7135	$173.71	$173.70	$173.70
Purchase #3	$111.55	3.554%	$115.5145	$115.51	$115.50	$115.50
Purchase #4	$20.81	3.371%	$21.5115	$21.51	$21.50	$21.50
Purchase #5	$129.76	7.177%	$139.0729	$139.07	$139.05	$139.10
Purchase #6	$125.87	12.707%	$141.8643	$141.86	$141.85	$141.90
Purchase #7	$122.50	4.793%	$128.3714	$128.37	$128.35	$128.40
7 purchase totals =	$759.31		$809.7557	$809.74	$809.65	$809.80