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	$42.41	3.552%	$43.9164	$43.92	$43.90	$43.90
Purchase #2	$95.27	13.642%	$108.2667	$108.27	$108.25	$108.30
Purchase #3	$43.47	8.417%	$47.1289	$47.13	$47.15	$47.10
Purchase #4	$12.83	6.563%	$13.672	$13.67	$13.65	$13.70
Purchase #5	$171.91	7.731%	$185.2004	$185.20	$185.20	$185.20
Purchase #6	$190.90	9.159%	$208.3845	$208.38	$208.40	$208.40
Purchase #7	$53.77	7.555%	$57.8323	$57.83	$57.85	$57.80
7 purchase totals =	$610.56		$664.4012	$664.40	$664.40	$664.40