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	$134.58	11.505%	$150.0634	$150.06	$150.05	$150.10
Purchase #2	$176.25	9.277%	$192.6007	$192.60	$192.60	$192.60
Purchase #3	$198.49	13.273%	$224.8356	$224.84	$224.85	$224.80
Purchase #4	$104.69	6.115%	$111.0918	$111.09	$111.10	$111.10
Purchase #5	$42.91	13.655%	$48.7694	$48.77	$48.75	$48.80
Purchase #6	$41.27	4.346%	$43.0636	$43.06	$43.05	$43.10
Purchase #7	$51.69	11.829%	$57.8044	$57.80	$57.80	$57.80
7 purchase totals =	$749.88		$828.2289	$828.22	$828.20	$828.30