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	$98.83	10.410%	$109.1182	$109.12	$109.10	$109.10
Purchase #2	$192.62	7.584%	$207.2283	$207.23	$207.25	$207.20
Purchase #3	$126.28	12.862%	$142.5221	$142.52	$142.50	$142.50
Purchase #4	$40.28	5.276%	$42.4052	$42.41	$42.40	$42.40
Purchase #5	$104.49	5.303%	$110.0311	$110.03	$110.05	$110.00
Purchase #6	$40.68	13.321%	$46.099	$46.10	$46.10	$46.10
Purchase #7	$133.70	7.289%	$143.4454	$143.45	$143.45	$143.40
7 purchase totals =	$736.88		$800.8493	$800.86	$800.85	$800.70