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	$166.30	12.276%	$186.715	$186.72	$186.70	$186.70
Purchase #2	$94.52	5.222%	$99.4558	$99.46	$99.45	$99.50
Purchase #3	$234.94	10.496%	$259.5993	$259.60	$259.60	$259.60
Purchase #4	$239.68	6.773%	$255.9135	$255.91	$255.90	$255.90
Purchase #5	$127.80	7.679%	$137.6138	$137.61	$137.60	$137.60
Purchase #6	$76.75	13.737%	$87.2931	$87.29	$87.30	$87.30
Purchase #7	$67.58	8.279%	$73.1749	$73.17	$73.15	$73.20
7 purchase totals =	$1,007.57		$1,099.7654	$1,099.76	$1,099.70	$1,099.80