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	$174.83	5.819%	$185.0034	$185.00	$185.00	$185.00
Purchase #2	$114.77	7.783%	$123.7025	$123.70	$123.70	$123.70
Purchase #3	$228.60	13.835%	$260.2268	$260.23	$260.25	$260.20
Purchase #4	$104.46	12.641%	$117.6648	$117.66	$117.65	$117.70
Purchase #5	$33.74	10.785%	$37.3789	$37.38	$37.40	$37.40
Purchase #6	$77.46	5.613%	$81.8078	$81.81	$81.80	$81.80
Purchase #7	$45.66	10.261%	$50.3452	$50.35	$50.35	$50.30
7 purchase totals =	$779.52		$856.1294	$856.13	$856.15	$856.10