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	$64.50	9.253%	$70.4682	$70.47	$70.45	$70.50
Purchase #2	$66.58	6.609%	$70.9803	$70.98	$71.00	$71.00
Purchase #3	$92.69	12.849%	$104.5997	$104.60	$104.60	$104.60
Purchase #4	$82.44	3.220%	$85.0946	$85.09	$85.10	$85.10
Purchase #5	$166.44	11.739%	$185.9784	$185.98	$186.00	$186.00
Purchase #6	$49.71	13.845%	$56.5923	$56.59	$56.60	$56.60
Purchase #7	$179.95	4.370%	$187.8138	$187.81	$187.80	$187.80
7 purchase totals =	$702.31		$761.5273	$761.52	$761.55	$761.60