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	$240.53	12.786%	$271.2842	$271.28	$271.30	$271.30
Purchase #2	$89.40	9.433%	$97.8331	$97.83	$97.85	$97.80
Purchase #3	$76.49	9.263%	$83.5753	$83.58	$83.60	$83.60
Purchase #4	$157.71	13.153%	$178.4536	$178.45	$178.45	$178.50
Purchase #5	$31.81	6.794%	$33.9712	$33.97	$33.95	$34.00
Purchase #6	$111.51	4.489%	$116.5157	$116.52	$116.50	$116.50
Purchase #7	$240.79	5.850%	$254.8762	$254.88	$254.90	$254.90
7 purchase totals =	$948.24		$1,036.5093	$1,036.51	$1,036.55	$1,036.60