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	$33.54	8.521%	$36.3979	$36.40	$36.40	$36.40
Purchase #2	$162.81	9.563%	$178.3795	$178.38	$178.40	$178.40
Purchase #3	$55.45	4.780%	$58.1005	$58.10	$58.10	$58.10
Purchase #4	$174.99	12.142%	$196.2373	$196.24	$196.25	$196.20
Purchase #5	$89.60	10.612%	$99.1084	$99.11	$99.10	$99.10
Purchase #6	$198.86	7.868%	$214.5063	$214.51	$214.50	$214.50
Purchase #7	$5.25	3.380%	$5.4275	$5.43	$5.45	$5.40
7 purchase totals =	$720.50		$788.1574	$788.17	$788.20	$788.10