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	$247.37	11.136%	$274.9171	$274.92	$274.90	$274.90
Purchase #2	$61.38	8.215%	$66.4224	$66.42	$66.40	$66.40
Purchase #3	$239.72	3.413%	$247.9016	$247.90	$247.90	$247.90
Purchase #4	$82.52	9.342%	$90.229	$90.23	$90.25	$90.20
Purchase #5	$233.61	9.810%	$256.5271	$256.53	$256.55	$256.50
Purchase #6	$166.95	6.536%	$177.8619	$177.86	$177.85	$177.90
Purchase #7	$118.58	5.727%	$125.3711	$125.37	$125.35	$125.40
7 purchase totals =	$1,150.13		$1,239.2302	$1,239.23	$1,239.20	$1,239.20