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	$48.30	12.706%	$54.437	$54.44	$54.45	$54.40
Purchase #2	$166.25	8.615%	$180.5724	$180.57	$180.55	$180.60
Purchase #3	$108.90	5.547%	$114.9407	$114.94	$114.95	$114.90
Purchase #4	$99.66	12.348%	$111.966	$111.97	$111.95	$112.00
Purchase #5	$197.82	13.529%	$224.5831	$224.58	$224.60	$224.60
Purchase #6	$180.41	8.831%	$196.342	$196.34	$196.35	$196.30
Purchase #7	$90.59	4.589%	$94.7472	$94.75	$94.75	$94.70
7 purchase totals =	$891.93		$977.5884	$977.59	$977.60	$977.50