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	$81.25	11.617%	$90.6888	$90.69	$90.70	$90.70
Purchase #2	$116.47	8.318%	$126.158	$126.16	$126.15	$126.20
Purchase #3	$241.97	13.224%	$273.9681	$273.97	$273.95	$274.00
Purchase #4	$133.94	13.446%	$151.9496	$151.95	$151.95	$151.90
Purchase #5	$237.27	13.422%	$269.1164	$269.12	$269.10	$269.10
Purchase #6	$47.89	6.149%	$50.8348	$50.83	$50.85	$50.80
Purchase #7	$185.53	6.728%	$198.0125	$198.01	$198.00	$198.00
7 purchase totals =	$1,044.32		$1,160.7282	$1,160.73	$1,160.70	$1,160.70