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	$85.35	5.209%	$89.7959	$89.80	$89.80	$89.80
Purchase #2	$37.27	5.565%	$39.3441	$39.34	$39.35	$39.30
Purchase #3	$66.87	8.212%	$72.3614	$72.36	$72.35	$72.40
Purchase #4	$192.26	11.471%	$214.3141	$214.31	$214.30	$214.30
Purchase #5	$19.66	6.259%	$20.8905	$20.89	$20.90	$20.90
Purchase #6	$29.41	12.416%	$33.0615	$33.06	$33.05	$33.10
Purchase #7	$171.85	12.727%	$193.7213	$193.72	$193.70	$193.70
7 purchase totals =	$602.67		$663.4888	$663.48	$663.45	$663.50