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	$20.47	4.174%	$21.3244	$21.32	$21.30	$21.30
Purchase #2	$111.96	13.122%	$126.6514	$126.65	$126.65	$126.70
Purchase #3	$209.88	11.724%	$234.4863	$234.49	$234.50	$234.50
Purchase #4	$64.55	4.384%	$67.3799	$67.38	$67.40	$67.40
Purchase #5	$112.47	10.130%	$123.8632	$123.86	$123.85	$123.90
Purchase #6	$157.52	9.226%	$172.0528	$172.05	$172.05	$172.10
Purchase #7	$135.56	12.388%	$152.3532	$152.35	$152.35	$152.40
7 purchase totals =	$812.41		$898.1112	$898.10	$898.10	$898.30