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	$123.32	11.630%	$137.6621	$137.66	$137.65	$137.70
Purchase #2	$124.54	4.750%	$130.4557	$130.46	$130.45	$130.50
Purchase #3	$247.93	12.727%	$279.4841	$279.48	$279.50	$279.50
Purchase #4	$139.62	10.578%	$154.389	$154.39	$154.40	$154.40
Purchase #5	$134.49	5.239%	$141.5359	$141.54	$141.55	$141.50
Purchase #6	$55.28	8.805%	$60.1474	$60.15	$60.15	$60.10
Purchase #7	$38.85	7.149%	$41.6274	$41.63	$41.65	$41.60
7 purchase totals =	$864.03		$945.3016	$945.31	$945.35	$945.30