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	$115.83	6.641%	$123.5223	$123.52	$123.50	$123.50
Purchase #2	$136.36	13.727%	$155.0781	$155.08	$155.10	$155.10
Purchase #3	$153.33	6.871%	$163.8653	$163.87	$163.85	$163.90
Purchase #4	$238.82	12.850%	$269.5084	$269.51	$269.50	$269.50
Purchase #5	$32.40	13.715%	$36.8437	$36.84	$36.85	$36.80
Purchase #6	$110.72	3.441%	$114.5299	$114.53	$114.55	$114.50
Purchase #7	$158.77	8.702%	$172.5862	$172.59	$172.60	$172.60
7 purchase totals =	$946.23		$1,035.9339	$1,035.94	$1,035.95	$1,035.90