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	$16.57	12.199%	$18.5914	$18.59	$18.60	$18.60
Purchase #2	$228.80	13.339%	$259.3196	$259.32	$259.30	$259.30
Purchase #3	$225.42	5.529%	$237.8835	$237.88	$237.90	$237.90
Purchase #4	$83.47	4.768%	$87.4498	$87.45	$87.45	$87.40
Purchase #5	$105.52	7.790%	$113.74	$113.74	$113.75	$113.70
Purchase #6	$243.56	9.662%	$267.0928	$267.09	$267.10	$267.10
Purchase #7	$115.59	10.345%	$127.5478	$127.55	$127.55	$127.50
7 purchase totals =	$1,018.93		$1,111.6249	$1,111.62	$1,111.65	$1,111.50