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	$38.90	10.149%	$42.848	$42.85	$42.85	$42.80
Purchase #2	$199.87	5.476%	$210.8149	$210.81	$210.80	$210.80
Purchase #3	$172.73	13.679%	$196.3577	$196.36	$196.35	$196.40
Purchase #4	$127.86	12.169%	$143.4193	$143.42	$143.40	$143.40
Purchase #5	$198.51	10.459%	$219.2722	$219.27	$219.25	$219.30
Purchase #6	$168.27	7.255%	$180.478	$180.48	$180.50	$180.50
Purchase #7	$248.69	13.264%	$281.6762	$281.68	$281.70	$281.70
7 purchase totals =	$1,154.83		$1,274.8663	$1,274.87	$1,274.85	$1,274.90