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	$45.53	6.540%	$48.5077	$48.51	$48.50	$48.50
Purchase #2	$92.35	11.525%	$102.9933	$102.99	$103.00	$103.00
Purchase #3	$141.60	4.643%	$148.1745	$148.17	$148.15	$148.20
Purchase #4	$59.79	6.265%	$63.5358	$63.54	$63.55	$63.50
Purchase #5	$218.89	10.715%	$242.3441	$242.34	$242.35	$242.30
Purchase #6	$118.93	7.541%	$127.8985	$127.90	$127.90	$127.90
Purchase #7	$38.73	12.666%	$43.6355	$43.64	$43.65	$43.60
7 purchase totals =	$715.82		$777.0894	$777.09	$777.10	$777.00