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	$93.88	12.656%	$105.7615	$105.76	$105.75	$105.80
Purchase #2	$38.34	10.155%	$42.2334	$42.23	$42.25	$42.20
Purchase #3	$9.79	10.855%	$10.8527	$10.85	$10.85	$10.90
Purchase #4	$181.86	10.106%	$200.2388	$200.24	$200.25	$200.20
Purchase #5	$86.84	3.624%	$89.9871	$89.99	$90.00	$90.00
Purchase #6	$20.66	4.744%	$21.6401	$21.64	$21.65	$21.60
Purchase #7	$185.68	3.448%	$192.0822	$192.08	$192.10	$192.10
7 purchase totals =	$617.05		$662.7958	$662.79	$662.85	$662.80