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	$246.83	10.602%	$272.9989	$273.00	$273.00	$273.00
Purchase #2	$103.85	7.439%	$111.5754	$111.58	$111.60	$111.60
Purchase #3	$151.69	13.693%	$172.4609	$172.46	$172.45	$172.50
Purchase #4	$172.75	3.438%	$178.6891	$178.69	$178.70	$178.70
Purchase #5	$81.90	12.682%	$92.2866	$92.29	$92.30	$92.30
Purchase #6	$130.38	9.261%	$142.4545	$142.45	$142.45	$142.50
Purchase #7	$222.98	5.785%	$235.8794	$235.88	$235.90	$235.90
7 purchase totals =	$1,110.38		$1,206.3448	$1,206.35	$1,206.40	$1,206.50