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	$13.90	9.833%	$15.2668	$15.27	$15.25	$15.30
Purchase #2	$43.99	8.837%	$47.8774	$47.88	$47.90	$47.90
Purchase #3	$17.82	8.757%	$19.3805	$19.38	$19.40	$19.40
Purchase #4	$152.53	12.853%	$172.1347	$172.13	$172.15	$172.10
Purchase #5	$184.32	9.847%	$202.47	$202.47	$202.45	$202.50
Purchase #6	$151.43	9.748%	$166.1914	$166.19	$166.20	$166.20
Purchase #7	$41.74	6.729%	$44.5487	$44.55	$44.55	$44.50
7 purchase totals =	$605.73		$667.8695	$667.87	$667.90	$667.90