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	$94.55	6.438%	$100.6371	$100.64	$100.65	$100.60
Purchase #2	$233.36	9.675%	$255.9376	$255.94	$255.95	$255.90
Purchase #3	$117.34	8.290%	$127.0675	$127.07	$127.05	$127.10
Purchase #4	$55.76	8.564%	$60.5353	$60.54	$60.55	$60.50
Purchase #5	$74.54	11.113%	$82.8236	$82.82	$82.80	$82.80
Purchase #6	$169.99	5.695%	$179.6709	$179.67	$179.65	$179.70
Purchase #7	$164.90	7.203%	$176.7777	$176.78	$176.80	$176.80
7 purchase totals =	$910.44		$983.4497	$983.46	$983.45	$983.40