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	$138.98	10.166%	$153.1087	$153.11	$153.10	$153.10
Purchase #2	$55.80	6.813%	$59.6017	$59.60	$59.60	$59.60
Purchase #3	$186.50	10.429%	$205.9501	$205.95	$205.95	$206.00
Purchase #4	$152.52	10.250%	$168.1533	$168.15	$168.15	$168.20
Purchase #5	$132.51	8.680%	$144.0119	$144.01	$144.00	$144.00
Purchase #6	$205.80	4.395%	$214.8449	$214.84	$214.85	$214.80
Purchase #7	$72.56	11.405%	$80.8355	$80.84	$80.85	$80.80
7 purchase totals =	$944.67		$1,026.5061	$1,026.50	$1,026.50	$1,026.50