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	$49.68	11.697%	$55.4911	$55.49	$55.50	$55.50
Purchase #2	$103.54	10.228%	$114.1301	$114.13	$114.15	$114.10
Purchase #3	$140.46	9.314%	$153.5424	$153.54	$153.55	$153.50
Purchase #4	$211.55	9.407%	$231.4505	$231.45	$231.45	$231.50
Purchase #5	$236.76	5.577%	$249.9641	$249.96	$249.95	$250.00
Purchase #6	$56.98	12.209%	$63.9367	$63.94	$63.95	$63.90
Purchase #7	$228.27	13.395%	$258.8468	$258.85	$258.85	$258.80
7 purchase totals =	$1,027.24		$1,127.3617	$1,127.36	$1,127.40	$1,127.30