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	$131.29	4.801%	$137.5932	$137.59	$137.60	$137.60
Purchase #2	$153.97	13.354%	$174.5312	$174.53	$174.55	$174.50
Purchase #3	$146.38	4.195%	$152.5206	$152.52	$152.50	$152.50
Purchase #4	$24.89	6.324%	$26.464	$26.46	$26.45	$26.50
Purchase #5	$196.94	13.638%	$223.7987	$223.80	$223.80	$223.80
Purchase #6	$107.89	8.564%	$117.1297	$117.13	$117.15	$117.10
Purchase #7	$65.96	13.584%	$74.92	$74.92	$74.90	$74.90
7 purchase totals =	$827.32		$906.9574	$906.95	$906.95	$906.90