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	$87.93	9.824%	$96.5682	$96.57	$96.55	$96.60
Purchase #2	$26.86	7.868%	$28.9733	$28.97	$28.95	$29.00
Purchase #3	$170.81	11.461%	$190.3865	$190.39	$190.40	$190.40
Purchase #4	$70.27	11.803%	$78.564	$78.56	$78.55	$78.60
Purchase #5	$246.97	3.510%	$255.6386	$255.64	$255.65	$255.60
Purchase #6	$109.41	3.592%	$113.34	$113.34	$113.35	$113.30
Purchase #7	$13.66	5.551%	$14.4183	$14.42	$14.40	$14.40
7 purchase totals =	$725.91		$777.8889	$777.89	$777.85	$777.90