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	$88.57	13.236%	$100.2931	$100.29	$100.30	$100.30
Purchase #2	$163.47	6.795%	$174.5778	$174.58	$174.60	$174.60
Purchase #3	$175.77	4.730%	$184.0839	$184.08	$184.10	$184.10
Purchase #4	$74.87	5.262%	$78.8097	$78.81	$78.80	$78.80
Purchase #5	$42.82	6.584%	$45.6393	$45.64	$45.65	$45.60
Purchase #6	$103.71	10.103%	$114.1878	$114.19	$114.20	$114.20
Purchase #7	$74.42	12.427%	$83.6682	$83.67	$83.65	$83.70
7 purchase totals =	$723.63		$781.2598	$781.26	$781.30	$781.30