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	$48.90	7.497%	$52.566	$52.57	$52.55	$52.60
Purchase #2	$112.47	13.790%	$127.9796	$127.98	$128.00	$128.00
Purchase #3	$114.54	7.236%	$122.8281	$122.83	$122.85	$122.80
Purchase #4	$158.31	13.271%	$179.3193	$179.32	$179.30	$179.30
Purchase #5	$55.77	5.640%	$58.9154	$58.92	$58.90	$58.90
Purchase #6	$230.89	11.534%	$257.5209	$257.52	$257.50	$257.50
Purchase #7	$123.38	12.845%	$139.2282	$139.23	$139.25	$139.20
7 purchase totals =	$844.26		$938.3575	$938.37	$938.35	$938.30