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	$100.40	6.354%	$106.7794	$106.78	$106.80	$106.80
Purchase #2	$138.73	8.493%	$150.5123	$150.51	$150.50	$150.50
Purchase #3	$250.41	7.373%	$268.8727	$268.87	$268.85	$268.90
Purchase #4	$18.28	3.844%	$18.9827	$18.98	$19.00	$19.00
Purchase #5	$185.88	12.325%	$208.7897	$208.79	$208.80	$208.80
Purchase #6	$157.31	3.331%	$162.55	$162.55	$162.55	$162.60
Purchase #7	$40.57	4.517%	$42.4025	$42.40	$42.40	$42.40
7 purchase totals =	$891.58		$958.8893	$958.88	$958.90	$959.00