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	$93.70	12.848%	$105.7386	$105.74	$105.75	$105.70
Purchase #2	$225.95	11.162%	$251.1705	$251.17	$251.15	$251.20
Purchase #3	$85.67	4.451%	$89.4832	$89.48	$89.50	$89.50
Purchase #4	$200.66	4.113%	$208.9131	$208.91	$208.90	$208.90
Purchase #5	$45.94	11.241%	$51.1041	$51.10	$51.10	$51.10
Purchase #6	$178.27	5.405%	$187.9055	$187.91	$187.90	$187.90
Purchase #7	$84.61	10.452%	$93.4534	$93.45	$93.45	$93.50
7 purchase totals =	$914.80		$987.7684	$987.76	$987.75	$987.80