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	$67.89	6.607%	$72.3755	$72.38	$72.40	$72.40
Purchase #2	$249.78	9.824%	$274.3184	$274.32	$274.30	$274.30
Purchase #3	$183.83	6.738%	$196.2165	$196.22	$196.20	$196.20
Purchase #4	$113.41	8.627%	$123.1939	$123.19	$123.20	$123.20
Purchase #5	$123.39	12.369%	$138.6521	$138.65	$138.65	$138.70
Purchase #6	$87.63	9.701%	$96.131	$96.13	$96.15	$96.10
Purchase #7	$179.99	13.390%	$204.0907	$204.09	$204.10	$204.10
7 purchase totals =	$1,005.92		$1,104.9781	$1,104.98	$1,105.00	$1,105.00