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	$163.69	10.494%	$180.8676	$180.87	$180.85	$180.90
Purchase #2	$179.75	12.615%	$202.4255	$202.43	$202.45	$202.40
Purchase #3	$100.55	9.243%	$109.8438	$109.84	$109.85	$109.80
Purchase #4	$37.80	13.678%	$42.9703	$42.97	$42.95	$43.00
Purchase #5	$195.88	13.539%	$222.4002	$222.40	$222.40	$222.40
Purchase #6	$41.60	9.610%	$45.5978	$45.60	$45.60	$45.60
Purchase #7	$77.75	9.634%	$85.2404	$85.24	$85.25	$85.20
7 purchase totals =	$797.02		$889.3456	$889.35	$889.35	$889.30