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	$47.77	5.178%	$50.2435	$50.24	$50.25	$50.20
Purchase #2	$131.50	10.168%	$144.8709	$144.87	$144.85	$144.90
Purchase #3	$52.82	10.659%	$58.4501	$58.45	$58.45	$58.50
Purchase #4	$115.34	7.852%	$124.3965	$124.40	$124.40	$124.40
Purchase #5	$213.53	12.592%	$240.4177	$240.42	$240.40	$240.40
Purchase #6	$136.66	8.808%	$148.697	$148.70	$148.70	$148.70
Purchase #7	$247.53	11.241%	$275.3548	$275.35	$275.35	$275.40
7 purchase totals =	$945.15		$1,042.4305	$1,042.43	$1,042.40	$1,042.50