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	$155.78	6.813%	$166.3933	$166.39	$166.40	$166.40
Purchase #2	$176.81	12.680%	$199.2295	$199.23	$199.25	$199.20
Purchase #3	$227.59	13.195%	$257.6205	$257.62	$257.60	$257.60
Purchase #4	$84.50	12.727%	$95.2543	$95.25	$95.25	$95.30
Purchase #5	$90.49	11.421%	$100.8249	$100.82	$100.80	$100.80
Purchase #6	$84.97	4.281%	$88.6076	$88.61	$88.60	$88.60
Purchase #7	$166.55	3.512%	$172.3992	$172.40	$172.40	$172.40
7 purchase totals =	$986.69		$1,080.3293	$1,080.32	$1,080.30	$1,080.30