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	$167.99	7.189%	$180.0668	$180.07	$180.05	$180.10
Purchase #2	$67.73	6.607%	$72.2049	$72.20	$72.20	$72.20
Purchase #3	$12.38	5.534%	$13.0651	$13.07	$13.05	$13.10
Purchase #4	$85.55	11.513%	$95.3994	$95.40	$95.40	$95.40
Purchase #5	$101.25	12.407%	$113.8121	$113.81	$113.80	$113.80
Purchase #6	$119.66	3.159%	$123.4401	$123.44	$123.45	$123.40
Purchase #7	$246.83	10.446%	$272.6139	$272.61	$272.60	$272.60
7 purchase totals =	$801.39		$870.6023	$870.60	$870.55	$870.60