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	$175.59	13.652%	$199.5615	$199.56	$199.55	$199.60
Purchase #2	$193.46	10.240%	$213.2703	$213.27	$213.25	$213.30
Purchase #3	$55.83	7.406%	$59.9648	$59.96	$59.95	$60.00
Purchase #4	$242.80	5.376%	$255.8529	$255.85	$255.85	$255.90
Purchase #5	$11.52	12.612%	$12.9729	$12.97	$12.95	$13.00
Purchase #6	$31.25	3.741%	$32.4191	$32.42	$32.40	$32.40
Purchase #7	$197.93	10.480%	$218.6731	$218.67	$218.65	$218.70
7 purchase totals =	$908.38		$992.7146	$992.70	$992.60	$992.90