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	$118.80	4.872%	$124.5879	$124.59	$124.60	$124.60
Purchase #2	$148.51	12.205%	$166.6356	$166.64	$166.65	$166.60
Purchase #3	$246.44	11.589%	$274.9999	$275.00	$275.00	$275.00
Purchase #4	$69.76	4.123%	$72.6362	$72.64	$72.65	$72.60
Purchase #5	$116.89	10.252%	$128.8736	$128.87	$128.85	$128.90
Purchase #6	$138.88	5.264%	$146.1906	$146.19	$146.20	$146.20
Purchase #7	$60.95	6.177%	$64.7149	$64.71	$64.70	$64.70
7 purchase totals =	$900.23		$978.6387	$978.64	$978.65	$978.60