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	$71.28	9.753%	$78.2319	$78.23	$78.25	$78.20
Purchase #2	$129.60	11.776%	$144.8617	$144.86	$144.85	$144.90
Purchase #3	$205.73	12.753%	$231.9667	$231.97	$231.95	$232.00
Purchase #4	$133.44	11.233%	$148.4293	$148.43	$148.45	$148.40
Purchase #5	$66.31	12.233%	$74.4217	$74.42	$74.40	$74.40
Purchase #6	$248.27	12.691%	$279.7779	$279.78	$279.80	$279.80
Purchase #7	$70.79	4.731%	$74.1391	$74.14	$74.15	$74.10
7 purchase totals =	$925.42		$1,031.8283	$1,031.83	$1,031.85	$1,031.80