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	$28.78	3.799%	$29.8734	$29.87	$29.85	$29.90
Purchase #2	$238.52	7.233%	$255.7722	$255.77	$255.75	$255.80
Purchase #3	$54.37	8.841%	$59.1769	$59.18	$59.20	$59.20
Purchase #4	$77.66	13.535%	$88.1713	$88.17	$88.15	$88.20
Purchase #5	$185.60	12.239%	$208.3156	$208.32	$208.30	$208.30
Purchase #6	$212.92	7.725%	$229.3681	$229.37	$229.35	$229.40
Purchase #7	$223.30	10.220%	$246.1213	$246.12	$246.10	$246.10
7 purchase totals =	$1,021.15		$1,116.7988	$1,116.80	$1,116.70	$1,116.90