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	$172.31	6.725%	$183.8978	$183.90	$183.90	$183.90
Purchase #2	$170.87	7.566%	$183.798	$183.80	$183.80	$183.80
Purchase #3	$107.62	3.273%	$111.1424	$111.14	$111.15	$111.10
Purchase #4	$79.32	3.689%	$82.2461	$82.25	$82.25	$82.20
Purchase #5	$172.87	9.692%	$189.6246	$189.62	$189.60	$189.60
Purchase #6	$62.37	13.183%	$70.5922	$70.59	$70.60	$70.60
Purchase #7	$136.30	9.106%	$148.7115	$148.71	$148.70	$148.70
7 purchase totals =	$901.66		$970.0126	$970.01	$970.00	$969.90