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	$93.34	10.704%	$103.3311	$103.33	$103.35	$103.30
Purchase #2	$214.60	10.674%	$237.5064	$237.51	$237.50	$237.50
Purchase #3	$173.61	7.814%	$187.1759	$187.18	$187.20	$187.20
Purchase #4	$17.64	12.739%	$19.8872	$19.89	$19.90	$19.90
Purchase #5	$227.49	13.246%	$257.6233	$257.62	$257.60	$257.60
Purchase #6	$132.84	8.837%	$144.5791	$144.58	$144.60	$144.60
Purchase #7	$54.80	8.416%	$59.412	$59.41	$59.40	$59.40
7 purchase totals =	$914.32		$1,009.5150	$1,009.52	$1,009.55	$1,009.50