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	$20.61	9.587%	$22.5859	$22.59	$22.60	$22.60
Purchase #2	$41.27	9.344%	$45.1263	$45.13	$45.15	$45.10
Purchase #3	$127.59	6.105%	$135.3794	$135.38	$135.40	$135.40
Purchase #4	$85.82	4.248%	$89.4656	$89.47	$89.45	$89.50
Purchase #5	$224.66	4.813%	$235.4729	$235.47	$235.45	$235.50
Purchase #6	$76.34	11.758%	$85.3161	$85.32	$85.30	$85.30
Purchase #7	$193.42	3.711%	$200.5978	$200.60	$200.60	$200.60
7 purchase totals =	$769.71		$813.9440	$813.96	$813.95	$814.00