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	$220.34	12.314%	$247.4727	$247.47	$247.45	$247.50
Purchase #2	$56.29	9.138%	$61.4338	$61.43	$61.45	$61.40
Purchase #3	$112.56	13.310%	$127.5417	$127.54	$127.55	$127.50
Purchase #4	$197.69	10.678%	$218.7993	$218.80	$218.80	$218.80
Purchase #5	$106.27	11.845%	$118.8577	$118.86	$118.85	$118.90
Purchase #6	$230.64	10.842%	$255.646	$255.65	$255.65	$255.60
Purchase #7	$43.52	10.129%	$47.9281	$47.93	$47.95	$47.90
7 purchase totals =	$967.31		$1,077.6793	$1,077.68	$1,077.70	$1,077.60