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	$227.38	5.500%	$239.8859	$239.89	$239.90	$239.90
Purchase #2	$53.86	11.219%	$59.9026	$59.90	$59.90	$59.90
Purchase #3	$154.96	7.861%	$167.1414	$167.14	$167.15	$167.10
Purchase #4	$127.79	8.731%	$138.9473	$138.95	$138.95	$138.90
Purchase #5	$15.49	9.548%	$16.969	$16.97	$16.95	$17.00
Purchase #6	$171.65	5.206%	$180.5861	$180.59	$180.60	$180.60
Purchase #7	$230.76	12.616%	$259.8727	$259.87	$259.85	$259.90
7 purchase totals =	$981.89		$1,063.3050	$1,063.31	$1,063.30	$1,063.30