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	$13.43	12.866%	$15.1579	$15.16	$15.15	$15.20
Purchase #2	$150.73	9.151%	$164.5233	$164.52	$164.50	$164.50
Purchase #3	$168.68	10.663%	$186.6663	$186.67	$186.65	$186.70
Purchase #4	$48.61	3.853%	$50.4829	$50.48	$50.50	$50.50
Purchase #5	$149.28	10.670%	$165.2082	$165.21	$165.20	$165.20
Purchase #6	$230.90	13.290%	$261.5866	$261.59	$261.60	$261.60
Purchase #7	$124.66	5.522%	$131.5437	$131.54	$131.55	$131.50
7 purchase totals =	$886.29		$975.1689	$975.17	$975.15	$975.20