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	$25.99	4.738%	$27.2214	$27.22	$27.20	$27.20
Purchase #2	$197.82	11.389%	$220.3497	$220.35	$220.35	$220.30
Purchase #3	$36.57	11.743%	$40.8644	$40.86	$40.85	$40.90
Purchase #4	$150.52	11.592%	$167.9683	$167.97	$167.95	$168.00
Purchase #5	$74.74	10.628%	$82.6834	$82.68	$82.70	$82.70
Purchase #6	$236.32	8.307%	$255.9511	$255.95	$255.95	$256.00
Purchase #7	$164.62	11.666%	$183.8246	$183.82	$183.80	$183.80
7 purchase totals =	$886.58		$978.8629	$978.85	$978.80	$978.90