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	$55.85	3.394%	$57.7455	$57.75	$57.75	$57.70
Purchase #2	$144.32	12.406%	$162.2243	$162.22	$162.20	$162.20
Purchase #3	$38.52	13.644%	$43.7757	$43.78	$43.80	$43.80
Purchase #4	$10.51	7.253%	$11.2723	$11.27	$11.25	$11.30
Purchase #5	$230.27	11.319%	$256.3343	$256.33	$256.35	$256.30
Purchase #6	$250.36	12.818%	$282.4511	$282.45	$282.45	$282.50
Purchase #7	$77.51	12.514%	$87.2096	$87.21	$87.20	$87.20
7 purchase totals =	$807.34		$901.0128	$901.01	$901.00	$901.00