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	$104.84	6.724%	$111.8894	$111.89	$111.90	$111.90
Purchase #2	$145.75	10.686%	$161.3248	$161.32	$161.30	$161.30
Purchase #3	$117.79	5.126%	$123.8279	$123.83	$123.85	$123.80
Purchase #4	$200.66	7.707%	$216.1249	$216.12	$216.10	$216.10
Purchase #5	$113.43	5.325%	$119.4701	$119.47	$119.45	$119.50
Purchase #6	$28.88	12.335%	$32.4423	$32.44	$32.45	$32.40
Purchase #7	$69.86	7.638%	$75.1959	$75.20	$75.20	$75.20
7 purchase totals =	$781.21		$840.2753	$840.27	$840.25	$840.20