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	$198.90	9.219%	$217.2366	$217.24	$217.25	$217.20
Purchase #2	$112.43	13.797%	$127.942	$127.94	$127.95	$127.90
Purchase #3	$109.86	12.604%	$123.7068	$123.71	$123.70	$123.70
Purchase #4	$11.86	7.325%	$12.7287	$12.73	$12.75	$12.70
Purchase #5	$111.29	11.630%	$124.233	$124.23	$124.25	$124.20
Purchase #6	$48.85	4.279%	$50.9403	$50.94	$50.95	$50.90
Purchase #7	$8.63	7.119%	$9.2444	$9.24	$9.25	$9.20
7 purchase totals =	$601.82		$666.0318	$666.03	$666.10	$665.80