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	$56.56	5.184%	$59.4921	$59.49	$59.50	$59.50
Purchase #2	$18.50	10.432%	$20.4299	$20.43	$20.45	$20.40
Purchase #3	$172.64	9.282%	$188.6644	$188.66	$188.65	$188.70
Purchase #4	$198.73	3.640%	$205.9638	$205.96	$205.95	$206.00
Purchase #5	$197.85	5.474%	$208.6803	$208.68	$208.70	$208.70
Purchase #6	$132.73	8.394%	$143.8714	$143.87	$143.85	$143.90
Purchase #7	$103.42	10.628%	$114.4115	$114.41	$114.40	$114.40
7 purchase totals =	$880.43		$941.5134	$941.50	$941.50	$941.60