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	$209.92	12.496%	$236.1516	$236.15	$236.15	$236.20
Purchase #2	$40.59	13.738%	$46.1663	$46.17	$46.15	$46.20
Purchase #3	$198.66	13.289%	$225.0599	$225.06	$225.05	$225.10
Purchase #4	$246.46	8.176%	$266.6106	$266.61	$266.60	$266.60
Purchase #5	$96.48	4.506%	$100.8274	$100.83	$100.85	$100.80
Purchase #6	$144.46	6.359%	$153.6462	$153.65	$153.65	$153.60
Purchase #7	$176.28	10.867%	$195.4363	$195.44	$195.45	$195.40
7 purchase totals =	$1,112.85		$1,223.8983	$1,223.91	$1,223.90	$1,223.90