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	$42.59	10.622%	$47.1139	$47.11	$47.10	$47.10
Purchase #2	$176.80	9.377%	$193.3785	$193.38	$193.40	$193.40
Purchase #3	$123.86	3.262%	$127.9003	$127.90	$127.90	$127.90
Purchase #4	$14.26	12.283%	$16.0116	$16.01	$16.00	$16.00
Purchase #5	$239.84	10.848%	$265.8578	$265.86	$265.85	$265.90
Purchase #6	$179.55	3.494%	$185.8235	$185.82	$185.80	$185.80
Purchase #7	$59.89	9.247%	$65.428	$65.43	$65.45	$65.40
7 purchase totals =	$836.79		$901.5136	$901.51	$901.50	$901.50