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	$47.25	10.312%	$52.1224	$52.12	$52.10	$52.10
Purchase #2	$136.37	10.479%	$150.6602	$150.66	$150.65	$150.70
Purchase #3	$146.30	6.870%	$156.3508	$156.35	$156.35	$156.40
Purchase #4	$108.71	4.130%	$113.1997	$113.20	$113.20	$113.20
Purchase #5	$103.49	12.844%	$116.7823	$116.78	$116.80	$116.80
Purchase #6	$33.74	12.423%	$37.9315	$37.93	$37.95	$37.90
Purchase #7	$52.42	11.536%	$58.4672	$58.47	$58.45	$58.50
7 purchase totals =	$628.28		$685.5141	$685.51	$685.50	$685.60