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	$24.86	3.152%	$25.6436	$25.64	$25.65	$25.60
Purchase #2	$36.97	13.859%	$42.0937	$42.09	$42.10	$42.10
Purchase #3	$12.91	9.484%	$14.1344	$14.13	$14.15	$14.10
Purchase #4	$245.32	8.252%	$265.5638	$265.56	$265.55	$265.60
Purchase #5	$121.62	4.479%	$127.0674	$127.07	$127.05	$127.10
Purchase #6	$170.60	11.190%	$189.6901	$189.69	$189.70	$189.70
Purchase #7	$165.84	5.676%	$175.2531	$175.25	$175.25	$175.30
7 purchase totals =	$778.12		$839.4461	$839.43	$839.45	$839.50