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	$225.44	10.364%	$248.8046	$248.80	$248.80	$248.80
Purchase #2	$221.79	6.789%	$236.8473	$236.85	$236.85	$236.80
Purchase #3	$52.88	9.735%	$58.0279	$58.03	$58.05	$58.00
Purchase #4	$66.42	9.305%	$72.6004	$72.60	$72.60	$72.60
Purchase #5	$79.45	13.749%	$90.3736	$90.37	$90.35	$90.40
Purchase #6	$74.77	5.123%	$78.6005	$78.60	$78.60	$78.60
Purchase #7	$44.30	4.613%	$46.3436	$46.34	$46.35	$46.30
7 purchase totals =	$765.05		$831.5979	$831.59	$831.60	$831.50