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	$51.47	11.573%	$57.4266	$57.43	$57.45	$57.40
Purchase #2	$233.34	4.480%	$243.7936	$243.79	$243.80	$243.80
Purchase #3	$160.49	3.691%	$166.4137	$166.41	$166.40	$166.40
Purchase #4	$54.47	3.247%	$56.2386	$56.24	$56.25	$56.20
Purchase #5	$123.72	4.682%	$129.5126	$129.51	$129.50	$129.50
Purchase #6	$106.69	4.579%	$111.5753	$111.58	$111.60	$111.60
Purchase #7	$141.64	13.753%	$161.1197	$161.12	$161.10	$161.10
7 purchase totals =	$871.82		$926.0801	$926.08	$926.10	$926.00