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	$220.90	9.366%	$241.5895	$241.59	$241.60	$241.60
Purchase #2	$200.37	7.248%	$214.8928	$214.89	$214.90	$214.90
Purchase #3	$240.81	12.706%	$271.4073	$271.41	$271.40	$271.40
Purchase #4	$21.96	10.342%	$24.2311	$24.23	$24.25	$24.20
Purchase #5	$216.55	9.796%	$237.7632	$237.76	$237.75	$237.80
Purchase #6	$52.32	9.205%	$57.1361	$57.14	$57.15	$57.10
Purchase #7	$24.49	5.692%	$25.884	$25.88	$25.90	$25.90
7 purchase totals =	$977.40		$1,072.9040	$1,072.90	$1,072.95	$1,072.90