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	$19.60	10.210%	$21.6012	$21.60	$21.60	$21.60
Purchase #2	$167.38	6.425%	$178.1342	$178.13	$178.15	$178.10
Purchase #3	$180.86	8.447%	$196.1372	$196.14	$196.15	$196.10
Purchase #4	$246.75	13.256%	$279.4592	$279.46	$279.45	$279.50
Purchase #5	$67.95	5.282%	$71.5391	$71.54	$71.55	$71.50
Purchase #6	$48.85	12.800%	$55.1028	$55.10	$55.10	$55.10
Purchase #7	$166.48	3.463%	$172.2452	$172.25	$172.25	$172.20
7 purchase totals =	$897.87		$974.2189	$974.22	$974.25	$974.10