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	$220.37	4.285%	$229.8129	$229.81	$229.80	$229.80
Purchase #2	$144.81	12.201%	$162.4783	$162.48	$162.50	$162.50
Purchase #3	$127.81	5.539%	$134.8894	$134.89	$134.90	$134.90
Purchase #4	$58.42	5.229%	$61.4748	$61.47	$61.45	$61.50
Purchase #5	$37.51	4.680%	$39.2655	$39.27	$39.25	$39.30
Purchase #6	$80.45	4.851%	$84.3526	$84.35	$84.35	$84.40
Purchase #7	$127.79	4.111%	$133.0434	$133.04	$133.05	$133.00
7 purchase totals =	$797.16		$845.3169	$845.31	$845.30	$845.40