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	$129.74	7.594%	$139.5925	$139.59	$139.60	$139.60
Purchase #2	$121.51	5.105%	$127.7131	$127.71	$127.70	$127.70
Purchase #3	$186.33	5.426%	$196.4403	$196.44	$196.45	$196.40
Purchase #4	$94.92	9.741%	$104.1662	$104.17	$104.15	$104.20
Purchase #5	$132.77	7.162%	$142.279	$142.28	$142.30	$142.30
Purchase #6	$248.51	6.824%	$265.4683	$265.47	$265.45	$265.50
Purchase #7	$100.32	10.334%	$110.6871	$110.69	$110.70	$110.70
7 purchase totals =	$1,014.10		$1,086.3465	$1,086.35	$1,086.35	$1,086.40