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	$123.41	13.472%	$140.0358	$140.04	$140.05	$140.00
Purchase #2	$117.97	4.332%	$123.0805	$123.08	$123.10	$123.10
Purchase #3	$210.83	7.775%	$227.222	$227.22	$227.20	$227.20
Purchase #4	$243.66	5.587%	$257.2733	$257.27	$257.25	$257.30
Purchase #5	$37.43	5.387%	$39.4464	$39.45	$39.45	$39.40
Purchase #6	$49.29	9.871%	$54.1554	$54.16	$54.15	$54.20
Purchase #7	$165.92	5.770%	$175.4936	$175.49	$175.50	$175.50
7 purchase totals =	$948.51		$1,016.7070	$1,016.71	$1,016.70	$1,016.70