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	$223.85	8.724%	$243.3787	$243.38	$243.40	$243.40
Purchase #2	$100.69	11.301%	$112.069	$112.07	$112.05	$112.10
Purchase #3	$71.71	12.143%	$80.4177	$80.42	$80.40	$80.40
Purchase #4	$74.92	6.372%	$79.6939	$79.69	$79.70	$79.70
Purchase #5	$225.54	11.169%	$250.7306	$250.73	$250.75	$250.70
Purchase #6	$56.28	12.786%	$63.476	$63.48	$63.50	$63.50
Purchase #7	$96.37	7.324%	$103.4281	$103.43	$103.45	$103.40
7 purchase totals =	$849.36		$933.1940	$933.20	$933.25	$933.20