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	$20.96	4.380%	$21.878	$21.88	$21.90	$21.90
Purchase #2	$167.69	3.670%	$173.8442	$173.84	$173.85	$173.80
Purchase #3	$48.38	11.759%	$54.069	$54.07	$54.05	$54.10
Purchase #4	$208.36	12.528%	$234.4633	$234.46	$234.45	$234.50
Purchase #5	$142.37	11.277%	$158.4251	$158.43	$158.45	$158.40
Purchase #6	$230.78	4.656%	$241.5251	$241.53	$241.55	$241.50
Purchase #7	$184.31	10.799%	$204.2136	$204.21	$204.20	$204.20
7 purchase totals =	$1,002.85		$1,088.4183	$1,088.42	$1,088.45	$1,088.40