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	$134.32	13.270%	$152.1443	$152.14	$152.15	$152.10
Purchase #2	$34.51	10.405%	$38.1008	$38.10	$38.10	$38.10
Purchase #3	$100.38	11.477%	$111.9006	$111.90	$111.90	$111.90
Purchase #4	$231.91	6.547%	$247.0931	$247.09	$247.10	$247.10
Purchase #5	$190.88	7.206%	$204.6348	$204.63	$204.65	$204.60
Purchase #6	$11.58	12.783%	$13.0603	$13.06	$13.05	$13.10
Purchase #7	$40.36	4.325%	$42.1056	$42.11	$42.10	$42.10
7 purchase totals =	$743.94		$809.0395	$809.03	$809.05	$809.00