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	$30.68	5.296%	$32.3048	$32.30	$32.30	$32.30
Purchase #2	$90.30	5.426%	$95.1997	$95.20	$95.20	$95.20
Purchase #3	$71.60	13.826%	$81.4994	$81.50	$81.50	$81.50
Purchase #4	$220.85	12.495%	$248.4452	$248.45	$248.45	$248.40
Purchase #5	$72.95	6.184%	$77.4612	$77.46	$77.45	$77.50
Purchase #6	$80.88	10.171%	$89.1063	$89.11	$89.10	$89.10
Purchase #7	$11.37	3.242%	$11.7386	$11.74	$11.75	$11.70
7 purchase totals =	$578.63		$635.7552	$635.76	$635.75	$635.70