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	$160.81	7.243%	$172.4575	$172.46	$172.45	$172.50
Purchase #2	$164.55	4.770%	$172.399	$172.40	$172.40	$172.40
Purchase #3	$76.88	5.129%	$80.8232	$80.82	$80.80	$80.80
Purchase #4	$18.80	8.170%	$20.336	$20.34	$20.35	$20.30
Purchase #5	$137.61	13.295%	$155.9052	$155.91	$155.90	$155.90
Purchase #6	$248.28	7.188%	$266.1264	$266.13	$266.15	$266.10
Purchase #7	$107.76	9.121%	$117.5888	$117.59	$117.60	$117.60
7 purchase totals =	$914.69		$985.6361	$985.65	$985.65	$985.60