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	$81.42	8.173%	$88.0745	$88.07	$88.05	$88.10
Purchase #2	$151.47	3.584%	$156.8987	$156.90	$156.90	$156.90
Purchase #3	$207.52	11.453%	$231.2873	$231.29	$231.30	$231.30
Purchase #4	$142.99	6.254%	$151.9326	$151.93	$151.95	$151.90
Purchase #5	$184.32	3.561%	$190.8836	$190.88	$190.90	$190.90
Purchase #6	$158.40	4.405%	$165.3775	$165.38	$165.40	$165.40
Purchase #7	$227.95	12.187%	$255.7303	$255.73	$255.75	$255.70
7 purchase totals =	$1,154.07		$1,240.1845	$1,240.18	$1,240.25	$1,240.20