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	$44.39	11.679%	$49.5743	$49.57	$49.55	$49.60
Purchase #2	$53.91	10.337%	$59.4827	$59.48	$59.50	$59.50
Purchase #3	$83.46	8.493%	$90.5483	$90.55	$90.55	$90.50
Purchase #4	$175.91	9.671%	$192.9223	$192.92	$192.90	$192.90
Purchase #5	$54.93	8.148%	$59.4057	$59.41	$59.40	$59.40
Purchase #6	$13.94	11.189%	$15.4997	$15.50	$15.50	$15.50
Purchase #7	$53.64	5.143%	$56.3987	$56.40	$56.40	$56.40
7 purchase totals =	$480.18		$523.8317	$523.83	$523.80	$523.80