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	$50.66	7.493%	$54.456	$54.46	$54.45	$54.50
Purchase #2	$159.45	11.822%	$178.3002	$178.30	$178.30	$178.30
Purchase #3	$43.57	4.136%	$45.3721	$45.37	$45.35	$45.40
Purchase #4	$125.65	9.480%	$137.5616	$137.56	$137.55	$137.60
Purchase #5	$87.73	13.390%	$99.477	$99.48	$99.50	$99.50
Purchase #6	$210.72	12.844%	$237.7849	$237.78	$237.80	$237.80
Purchase #7	$138.81	10.221%	$152.9978	$153.00	$153.00	$153.00
7 purchase totals =	$816.59		$905.9496	$905.95	$905.95	$906.10