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	$10.34	11.381%	$11.5168	$11.52	$11.50	$11.50
Purchase #2	$175.25	3.747%	$181.8166	$181.82	$181.80	$181.80
Purchase #3	$123.41	12.542%	$138.8881	$138.89	$138.90	$138.90
Purchase #4	$138.49	3.712%	$143.6307	$143.63	$143.65	$143.60
Purchase #5	$182.60	13.311%	$206.9059	$206.91	$206.90	$206.90
Purchase #6	$239.90	13.512%	$272.3153	$272.32	$272.30	$272.30
Purchase #7	$134.91	3.168%	$139.1839	$139.18	$139.20	$139.20
7 purchase totals =	$1,004.90		$1,094.2573	$1,094.27	$1,094.25	$1,094.20