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	$138.51	8.303%	$150.0105	$150.01	$150.00	$150.00
Purchase #2	$221.39	8.576%	$240.3764	$240.38	$240.40	$240.40
Purchase #3	$111.29	10.300%	$122.7529	$122.75	$122.75	$122.80
Purchase #4	$48.83	8.125%	$52.7974	$52.80	$52.80	$52.80
Purchase #5	$89.88	11.347%	$100.0787	$100.08	$100.10	$100.10
Purchase #6	$157.52	3.238%	$162.6205	$162.62	$162.60	$162.60
Purchase #7	$102.84	10.460%	$113.5971	$113.60	$113.60	$113.60
7 purchase totals =	$870.26		$942.2335	$942.24	$942.25	$942.30