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	$51.94	4.649%	$54.3547	$54.35	$54.35	$54.40
Purchase #2	$142.25	11.329%	$158.3655	$158.37	$158.35	$158.40
Purchase #3	$20.43	3.804%	$21.2072	$21.21	$21.20	$21.20
Purchase #4	$170.96	10.280%	$188.5347	$188.53	$188.55	$188.50
Purchase #5	$74.94	11.447%	$83.5184	$83.52	$83.50	$83.50
Purchase #6	$132.59	3.513%	$137.2479	$137.25	$137.25	$137.20
Purchase #7	$130.28	10.531%	$143.9998	$144.00	$144.00	$144.00
7 purchase totals =	$723.39		$787.2282	$787.23	$787.20	$787.20