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	$127.36	9.354%	$139.2733	$139.27	$139.25	$139.30
Purchase #2	$195.69	11.458%	$218.1122	$218.11	$218.10	$218.10
Purchase #3	$62.87	13.605%	$71.4235	$71.42	$71.40	$71.40
Purchase #4	$34.33	10.244%	$37.8468	$37.85	$37.85	$37.80
Purchase #5	$7.63	6.595%	$8.1332	$8.13	$8.15	$8.10
Purchase #6	$200.68	4.149%	$209.0062	$209.01	$209.00	$209.00
Purchase #7	$43.55	4.308%	$45.4261	$45.43	$45.45	$45.40
7 purchase totals =	$672.11		$729.2213	$729.22	$729.20	$729.10