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	$152.85	4.383%	$159.5494	$159.55	$159.55	$159.50
Purchase #2	$119.83	5.311%	$126.1942	$126.19	$126.20	$126.20
Purchase #3	$75.93	3.146%	$78.3188	$78.32	$78.30	$78.30
Purchase #4	$88.62	13.716%	$100.7751	$100.78	$100.80	$100.80
Purchase #5	$114.75	10.717%	$127.0478	$127.05	$127.05	$127.00
Purchase #6	$61.38	5.339%	$64.6571	$64.66	$64.65	$64.70
Purchase #7	$31.61	5.483%	$33.3432	$33.34	$33.35	$33.30
7 purchase totals =	$644.97		$689.8856	$689.89	$689.90	$689.80