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	$55.27	12.124%	$61.9709	$61.97	$61.95	$62.00
Purchase #2	$40.71	10.259%	$44.8864	$44.89	$44.90	$44.90
Purchase #3	$114.31	6.865%	$122.1574	$122.16	$122.15	$122.20
Purchase #4	$97.81	6.194%	$103.8684	$103.87	$103.85	$103.90
Purchase #5	$123.39	9.844%	$135.5365	$135.54	$135.55	$135.50
Purchase #6	$222.60	4.733%	$233.1357	$233.14	$233.15	$233.10
Purchase #7	$67.69	5.334%	$71.3006	$71.30	$71.30	$71.30
7 purchase totals =	$721.78		$772.8559	$772.87	$772.85	$772.90