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	$20.46	7.737%	$22.043	$22.04	$22.05	$22.00
Purchase #2	$124.87	10.180%	$137.5818	$137.58	$137.60	$137.60
Purchase #3	$82.77	8.746%	$90.0091	$90.01	$90.00	$90.00
Purchase #4	$94.54	11.545%	$105.4546	$105.45	$105.45	$105.50
Purchase #5	$194.53	5.170%	$204.5872	$204.59	$204.60	$204.60
Purchase #6	$226.94	5.784%	$240.0662	$240.07	$240.05	$240.10
Purchase #7	$185.67	11.800%	$207.5791	$207.58	$207.60	$207.60
7 purchase totals =	$929.78		$1,007.3210	$1,007.32	$1,007.35	$1,007.40