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	$123.56	3.457%	$127.8315	$127.83	$127.85	$127.80
Purchase #2	$143.86	9.228%	$157.1354	$157.14	$157.15	$157.10
Purchase #3	$24.92	6.428%	$26.5219	$26.52	$26.50	$26.50
Purchase #4	$53.69	10.421%	$59.285	$59.29	$59.30	$59.30
Purchase #5	$159.69	12.444%	$179.5618	$179.56	$179.55	$179.60
Purchase #6	$45.56	5.653%	$48.1355	$48.14	$48.15	$48.10
Purchase #7	$47.84	7.838%	$51.5897	$51.59	$51.60	$51.60
7 purchase totals =	$599.12		$650.0608	$650.07	$650.10	$650.00