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	$85.82	5.487%	$90.5289	$90.53	$90.55	$90.50
Purchase #2	$153.59	9.243%	$167.7863	$167.79	$167.80	$167.80
Purchase #3	$106.40	10.106%	$117.1528	$117.15	$117.15	$117.20
Purchase #4	$150.82	3.295%	$155.7895	$155.79	$155.80	$155.80
Purchase #5	$109.50	4.488%	$114.4144	$114.41	$114.40	$114.40
Purchase #6	$44.92	12.868%	$50.7003	$50.70	$50.70	$50.70
Purchase #7	$167.43	8.716%	$182.0232	$182.02	$182.00	$182.00
7 purchase totals =	$818.48		$878.3954	$878.39	$878.40	$878.40