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	$29.79	11.421%	$33.1923	$33.19	$33.20	$33.20
Purchase #2	$152.59	12.376%	$171.4745	$171.47	$171.45	$171.50
Purchase #3	$178.80	5.256%	$188.1977	$188.20	$188.20	$188.20
Purchase #4	$114.25	11.855%	$127.7943	$127.79	$127.80	$127.80
Purchase #5	$230.72	8.373%	$250.0382	$250.04	$250.05	$250.00
Purchase #6	$154.47	6.554%	$164.594	$164.59	$164.60	$164.60
Purchase #7	$139.51	6.203%	$148.1638	$148.16	$148.15	$148.20
7 purchase totals =	$1,000.13		$1,083.4548	$1,083.44	$1,083.45	$1,083.50