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	$75.38	6.329%	$80.1508	$80.15	$80.15	$80.20
Purchase #2	$171.70	11.300%	$191.1021	$191.10	$191.10	$191.10
Purchase #3	$231.35	13.391%	$262.3301	$262.33	$262.35	$262.30
Purchase #4	$192.34	4.284%	$200.5798	$200.58	$200.60	$200.60
Purchase #5	$44.69	9.803%	$49.071	$49.07	$49.05	$49.10
Purchase #6	$241.45	5.637%	$255.0605	$255.06	$255.05	$255.10
Purchase #7	$127.47	4.397%	$133.0749	$133.07	$133.05	$133.10
7 purchase totals =	$1,084.38		$1,171.3692	$1,171.36	$1,171.35	$1,171.50