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	$128.48	13.222%	$145.4676	$145.47	$145.45	$145.50
Purchase #2	$157.45	11.174%	$175.0435	$175.04	$175.05	$175.00
Purchase #3	$41.29	9.140%	$45.0639	$45.06	$45.05	$45.10
Purchase #4	$135.37	7.577%	$145.627	$145.63	$145.65	$145.60
Purchase #5	$48.99	8.286%	$53.0493	$53.05	$53.05	$53.00
Purchase #6	$12.30	9.654%	$13.4874	$13.49	$13.50	$13.50
Purchase #7	$86.93	3.358%	$89.8491	$89.85	$89.85	$89.80
7 purchase totals =	$610.81		$667.5878	$667.59	$667.60	$667.50