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	$145.89	7.276%	$156.505	$156.51	$156.50	$156.50
Purchase #2	$228.35	13.792%	$259.844	$259.84	$259.85	$259.80
Purchase #3	$59.60	8.108%	$64.4324	$64.43	$64.45	$64.40
Purchase #4	$74.71	6.455%	$79.5325	$79.53	$79.55	$79.50
Purchase #5	$204.64	4.490%	$213.8283	$213.83	$213.85	$213.80
Purchase #6	$185.30	3.336%	$191.4816	$191.48	$191.50	$191.50
Purchase #7	$228.78	10.548%	$252.9117	$252.91	$252.90	$252.90
7 purchase totals =	$1,127.27		$1,218.5355	$1,218.53	$1,218.60	$1,218.40