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	$80.84	10.591%	$89.4018	$89.40	$89.40	$89.40
Purchase #2	$71.57	8.779%	$77.8531	$77.85	$77.85	$77.90
Purchase #3	$124.77	4.712%	$130.6492	$130.65	$130.65	$130.60
Purchase #4	$246.58	13.117%	$278.9239	$278.92	$278.90	$278.90
Purchase #5	$120.87	10.114%	$133.0948	$133.09	$133.10	$133.10
Purchase #6	$248.95	9.297%	$272.0949	$272.09	$272.10	$272.10
Purchase #7	$13.65	12.656%	$15.3775	$15.38	$15.40	$15.40
7 purchase totals =	$907.23		$997.3952	$997.38	$997.40	$997.40