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	$83.80	6.768%	$89.4716	$89.47	$89.45	$89.50
Purchase #2	$21.87	10.618%	$24.1922	$24.19	$24.20	$24.20
Purchase #3	$123.68	7.335%	$132.7519	$132.75	$132.75	$132.80
Purchase #4	$102.56	9.108%	$111.9012	$111.90	$111.90	$111.90
Purchase #5	$186.27	5.634%	$196.7645	$196.76	$196.75	$196.80
Purchase #6	$27.70	3.556%	$28.685	$28.69	$28.70	$28.70
Purchase #7	$148.39	12.302%	$166.6449	$166.64	$166.65	$166.60
7 purchase totals =	$694.27		$750.4113	$750.40	$750.40	$750.50