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	$131.77	6.186%	$139.9213	$139.92	$139.90	$139.90
Purchase #2	$244.68	4.420%	$255.4949	$255.49	$255.50	$255.50
Purchase #3	$173.69	13.579%	$197.2754	$197.28	$197.30	$197.30
Purchase #4	$207.92	3.735%	$215.6858	$215.69	$215.70	$215.70
Purchase #5	$240.29	3.576%	$248.8828	$248.88	$248.90	$248.90
Purchase #6	$74.28	9.623%	$81.428	$81.43	$81.45	$81.40
Purchase #7	$74.91	4.822%	$78.5222	$78.52	$78.50	$78.50
7 purchase totals =	$1,147.54		$1,217.2104	$1,217.21	$1,217.25	$1,217.20