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	$93.31	11.545%	$104.0826	$104.08	$104.10	$104.10
Purchase #2	$153.40	9.197%	$167.5082	$167.51	$167.50	$167.50
Purchase #3	$5.63	8.297%	$6.0971	$6.10	$6.10	$6.10
Purchase #4	$110.42	11.835%	$123.4882	$123.49	$123.50	$123.50
Purchase #5	$89.61	13.620%	$101.8149	$101.81	$101.80	$101.80
Purchase #6	$15.92	13.268%	$18.0323	$18.03	$18.05	$18.00
Purchase #7	$95.72	4.655%	$100.1758	$100.18	$100.20	$100.20
7 purchase totals =	$564.01		$621.1991	$621.20	$621.25	$621.20