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	$238.44	13.140%	$269.771	$269.77	$269.75	$269.80
Purchase #2	$86.87	3.526%	$89.933	$89.93	$89.95	$89.90
Purchase #3	$145.71	10.106%	$160.4355	$160.44	$160.45	$160.40
Purchase #4	$127.90	8.265%	$138.4709	$138.47	$138.45	$138.50
Purchase #5	$31.51	5.103%	$33.118	$33.12	$33.10	$33.10
Purchase #6	$167.97	13.378%	$190.441	$190.44	$190.45	$190.40
Purchase #7	$245.86	5.364%	$259.0479	$259.05	$259.05	$259.00
7 purchase totals =	$1,044.26		$1,141.2173	$1,141.22	$1,141.20	$1,141.10