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	$182.90	3.286%	$188.9101	$188.91	$188.90	$188.90
Purchase #2	$249.52	8.157%	$269.8733	$269.87	$269.85	$269.90
Purchase #3	$86.50	4.150%	$90.0898	$90.09	$90.10	$90.10
Purchase #4	$79.67	9.811%	$87.4864	$87.49	$87.50	$87.50
Purchase #5	$45.40	4.553%	$47.4671	$47.47	$47.45	$47.50
Purchase #6	$118.28	4.670%	$123.8037	$123.80	$123.80	$123.80
Purchase #7	$249.93	11.721%	$279.2243	$279.22	$279.20	$279.20
7 purchase totals =	$1,012.20		$1,086.8547	$1,086.85	$1,086.80	$1,086.90