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	$84.97	6.501%	$90.4939	$90.49	$90.50	$90.50
Purchase #2	$62.59	3.143%	$64.5572	$64.56	$64.55	$64.60
Purchase #3	$153.45	5.261%	$161.523	$161.52	$161.50	$161.50
Purchase #4	$199.77	4.308%	$208.3761	$208.38	$208.40	$208.40
Purchase #5	$127.89	12.650%	$144.0681	$144.07	$144.05	$144.10
Purchase #6	$108.41	4.375%	$113.1529	$113.15	$113.15	$113.20
Purchase #7	$127.56	4.767%	$133.6408	$133.64	$133.65	$133.60
7 purchase totals =	$864.64		$915.8120	$915.81	$915.80	$915.90