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	$28.27	5.687%	$29.8777	$29.88	$29.90	$29.90
Purchase #2	$87.75	3.697%	$90.9941	$90.99	$91.00	$91.00
Purchase #3	$157.33	13.341%	$178.3194	$178.32	$178.30	$178.30
Purchase #4	$210.26	9.127%	$229.4504	$229.45	$229.45	$229.50
Purchase #5	$170.85	5.107%	$179.5753	$179.58	$179.60	$179.60
Purchase #6	$231.29	12.783%	$260.8558	$260.86	$260.85	$260.90
Purchase #7	$83.51	8.499%	$90.6075	$90.61	$90.60	$90.60
7 purchase totals =	$969.26		$1,059.6802	$1,059.69	$1,059.70	$1,059.80