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	$138.47	12.716%	$156.0778	$156.08	$156.10	$156.10
Purchase #2	$126.29	4.210%	$131.6068	$131.61	$131.60	$131.60
Purchase #3	$143.40	3.806%	$148.8578	$148.86	$148.85	$148.90
Purchase #4	$173.50	6.808%	$185.3119	$185.31	$185.30	$185.30
Purchase #5	$36.26	11.780%	$40.5314	$40.53	$40.55	$40.50
Purchase #6	$57.53	8.795%	$62.5898	$62.59	$62.60	$62.60
Purchase #7	$110.77	12.124%	$124.1998	$124.20	$124.20	$124.20
7 purchase totals =	$786.22		$849.1753	$849.18	$849.20	$849.20