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	$77.29	4.840%	$81.0308	$81.03	$81.05	$81.00
Purchase #2	$97.99	11.712%	$109.4666	$109.47	$109.45	$109.50
Purchase #3	$58.66	13.545%	$66.6055	$66.61	$66.60	$66.60
Purchase #4	$38.28	5.813%	$40.5052	$40.51	$40.50	$40.50
Purchase #5	$204.41	6.769%	$218.2465	$218.25	$218.25	$218.20
Purchase #6	$186.70	9.746%	$204.8958	$204.90	$204.90	$204.90
Purchase #7	$100.59	10.829%	$111.4829	$111.48	$111.50	$111.50
7 purchase totals =	$763.92		$832.2333	$832.25	$832.25	$832.20