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	$207.76	8.384%	$225.1786	$225.18	$225.20	$225.20
Purchase #2	$168.75	5.516%	$178.0583	$178.06	$178.05	$178.10
Purchase #3	$138.29	4.337%	$144.2876	$144.29	$144.30	$144.30
Purchase #4	$201.89	11.652%	$225.4142	$225.41	$225.40	$225.40
Purchase #5	$223.60	8.294%	$242.1454	$242.15	$242.15	$242.10
Purchase #6	$88.89	6.619%	$94.7736	$94.77	$94.75	$94.80
Purchase #7	$12.64	5.630%	$13.3516	$13.35	$13.35	$13.40
7 purchase totals =	$1,041.82		$1,123.2093	$1,123.21	$1,123.20	$1,123.30