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	$244.69	13.798%	$278.4523	$278.45	$278.45	$278.50
Purchase #2	$39.35	3.773%	$40.8347	$40.83	$40.85	$40.80
Purchase #3	$148.59	7.154%	$159.2201	$159.22	$159.20	$159.20
Purchase #4	$21.25	5.803%	$22.4831	$22.48	$22.50	$22.50
Purchase #5	$121.83	12.278%	$136.7883	$136.79	$136.80	$136.80
Purchase #6	$99.84	10.103%	$109.9268	$109.93	$109.95	$109.90
Purchase #7	$241.54	12.268%	$271.1721	$271.17	$271.15	$271.20
7 purchase totals =	$917.09		$1,018.8774	$1,018.87	$1,018.90	$1,018.90