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	$12.45	3.473%	$12.8824	$12.88	$12.90	$12.90
Purchase #2	$143.27	3.778%	$148.6827	$148.68	$148.70	$148.70
Purchase #3	$248.49	5.174%	$261.3469	$261.35	$261.35	$261.30
Purchase #4	$168.69	8.734%	$183.4234	$183.42	$183.40	$183.40
Purchase #5	$224.79	13.188%	$254.4353	$254.44	$254.45	$254.40
Purchase #6	$85.66	4.405%	$89.4333	$89.43	$89.45	$89.40
Purchase #7	$203.81	13.513%	$231.3508	$231.35	$231.35	$231.40
7 purchase totals =	$1,087.16		$1,181.5548	$1,181.55	$1,181.60	$1,181.50