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	$89.49	12.378%	$100.5671	$100.57	$100.55	$100.60
Purchase #2	$80.50	4.142%	$83.8343	$83.83	$83.85	$83.80
Purchase #3	$51.25	3.339%	$52.9612	$52.96	$52.95	$53.00
Purchase #4	$13.45	12.243%	$15.0967	$15.10	$15.10	$15.10
Purchase #5	$20.45	9.150%	$22.3212	$22.32	$22.30	$22.30
Purchase #6	$90.63	10.866%	$100.4779	$100.48	$100.50	$100.50
Purchase #7	$175.73	12.115%	$197.0197	$197.02	$197.00	$197.00
7 purchase totals =	$521.50		$572.2781	$572.28	$572.25	$572.30