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	$223.75	11.452%	$249.3739	$249.37	$249.35	$249.40
Purchase #2	$113.84	12.574%	$128.1542	$128.15	$128.15	$128.20
Purchase #3	$124.40	6.217%	$132.1339	$132.13	$132.15	$132.10
Purchase #4	$83.95	6.609%	$89.4983	$89.50	$89.50	$89.50
Purchase #5	$52.51	8.138%	$56.7833	$56.78	$56.80	$56.80
Purchase #6	$68.78	10.619%	$76.0837	$76.08	$76.10	$76.10
Purchase #7	$127.81	13.727%	$145.3545	$145.35	$145.35	$145.40
7 purchase totals =	$795.04		$877.3818	$877.36	$877.40	$877.50