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	$38.54	6.490%	$41.0412	$41.04	$41.05	$41.00
Purchase #2	$112.78	6.214%	$119.7881	$119.79	$119.80	$119.80
Purchase #3	$40.75	5.127%	$42.8393	$42.84	$42.85	$42.80
Purchase #4	$85.63	13.239%	$96.9666	$96.97	$96.95	$97.00
Purchase #5	$176.30	9.395%	$192.8634	$192.86	$192.85	$192.90
Purchase #6	$72.87	7.742%	$78.5116	$78.51	$78.50	$78.50
Purchase #7	$15.43	11.308%	$17.1748	$17.17	$17.15	$17.20
7 purchase totals =	$542.30		$589.1850	$589.18	$589.15	$589.20