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	$37.59	9.418%	$41.1302	$41.13	$41.15	$41.10
Purchase #2	$131.47	10.196%	$144.8747	$144.87	$144.85	$144.90
Purchase #3	$239.66	11.799%	$267.9375	$267.94	$267.95	$267.90
Purchase #4	$175.87	8.274%	$190.4215	$190.42	$190.40	$190.40
Purchase #5	$144.62	8.445%	$156.8332	$156.83	$156.85	$156.80
Purchase #6	$128.90	5.709%	$136.2589	$136.26	$136.25	$136.30
Purchase #7	$12.37	6.156%	$13.1315	$13.13	$13.15	$13.10
7 purchase totals =	$870.48		$950.5875	$950.58	$950.60	$950.50