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	$77.55	6.776%	$82.8048	$82.80	$82.80	$82.80
Purchase #2	$141.26	5.210%	$148.6196	$148.62	$148.60	$148.60
Purchase #3	$192.96	10.753%	$213.709	$213.71	$213.70	$213.70
Purchase #4	$96.33	9.142%	$105.1365	$105.14	$105.15	$105.10
Purchase #5	$10.74	7.789%	$11.5765	$11.58	$11.60	$11.60
Purchase #6	$78.74	13.796%	$89.603	$89.60	$89.60	$89.60
Purchase #7	$228.52	12.636%	$257.3958	$257.40	$257.40	$257.40
7 purchase totals =	$826.10		$908.8452	$908.85	$908.85	$908.80