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	$24.54	5.231%	$25.8237	$25.82	$25.80	$25.80
Purchase #2	$87.34	3.549%	$90.4397	$90.44	$90.45	$90.40
Purchase #3	$140.39	8.480%	$152.2951	$152.30	$152.30	$152.30
Purchase #4	$177.32	12.442%	$199.3822	$199.38	$199.40	$199.40
Purchase #5	$6.84	8.768%	$7.4397	$7.44	$7.45	$7.40
Purchase #6	$32.25	3.196%	$33.2807	$33.28	$33.30	$33.30
Purchase #7	$29.88	8.125%	$32.3078	$32.31	$32.30	$32.30
7 purchase totals =	$498.56		$540.9689	$540.97	$541.00	$540.90