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	$13.94	10.123%	$15.3511	$15.35	$15.35	$15.40
Purchase #2	$98.27	7.496%	$105.6363	$105.64	$105.65	$105.60
Purchase #3	$34.72	7.162%	$37.2066	$37.21	$37.20	$37.20
Purchase #4	$224.96	12.692%	$253.5119	$253.51	$253.50	$253.50
Purchase #5	$206.44	13.778%	$234.8833	$234.88	$234.90	$234.90
Purchase #6	$107.27	5.274%	$112.9274	$112.93	$112.95	$112.90
Purchase #7	$231.47	11.710%	$258.5751	$258.58	$258.60	$258.60
7 purchase totals =	$917.07		$1,018.0917	$1,018.10	$1,018.15	$1,018.10