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	$39.60	13.415%	$44.9123	$44.91	$44.90	$44.90
Purchase #2	$111.41	9.631%	$122.1399	$122.14	$122.15	$122.10
Purchase #3	$149.71	12.128%	$167.8668	$167.87	$167.85	$167.90
Purchase #4	$104.90	8.213%	$113.5154	$113.52	$113.50	$113.50
Purchase #5	$76.55	11.187%	$85.1136	$85.11	$85.10	$85.10
Purchase #6	$128.71	11.484%	$143.4911	$143.49	$143.50	$143.50
Purchase #7	$48.52	10.382%	$53.5573	$53.56	$53.55	$53.60
7 purchase totals =	$659.40		$730.5964	$730.60	$730.55	$730.60