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	$130.81	7.104%	$140.1027	$140.10	$140.10	$140.10
Purchase #2	$236.46	3.476%	$244.6793	$244.68	$244.70	$244.70
Purchase #3	$240.82	10.396%	$265.8556	$265.86	$265.85	$265.90
Purchase #4	$111.61	11.806%	$124.7867	$124.79	$124.80	$124.80
Purchase #5	$107.27	8.144%	$116.0061	$116.01	$116.00	$116.00
Purchase #6	$244.93	4.462%	$255.8588	$255.86	$255.85	$255.90
Purchase #7	$186.34	5.540%	$196.6632	$196.66	$196.65	$196.70
7 purchase totals =	$1,258.24		$1,343.9524	$1,343.96	$1,343.95	$1,344.10