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	$25.84	9.418%	$28.2736	$28.27	$28.25	$28.30
Purchase #2	$107.40	3.557%	$111.2202	$111.22	$111.20	$111.20
Purchase #3	$171.74	9.426%	$187.9282	$187.93	$187.95	$187.90
Purchase #4	$38.50	12.360%	$43.2586	$43.26	$43.25	$43.30
Purchase #5	$179.44	10.672%	$198.5898	$198.59	$198.60	$198.60
Purchase #6	$233.32	6.778%	$249.1344	$249.13	$249.15	$249.10
Purchase #7	$115.93	9.606%	$127.0662	$127.07	$127.05	$127.10
7 purchase totals =	$872.17		$945.4710	$945.47	$945.45	$945.50