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	$123.40	9.129%	$134.6652	$134.67	$134.65	$134.70
Purchase #2	$122.52	4.325%	$127.819	$127.82	$127.80	$127.80
Purchase #3	$127.48	3.327%	$131.7213	$131.72	$131.70	$131.70
Purchase #4	$130.59	8.166%	$141.254	$141.25	$141.25	$141.30
Purchase #5	$80.75	10.778%	$89.4532	$89.45	$89.45	$89.50
Purchase #6	$192.88	6.395%	$205.2147	$205.21	$205.20	$205.20
Purchase #7	$182.32	8.720%	$198.2183	$198.22	$198.20	$198.20
7 purchase totals =	$959.94		$1,028.3457	$1,028.34	$1,028.25	$1,028.40