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	$84.84	6.395%	$90.2655	$90.27	$90.25	$90.30
Purchase #2	$133.75	4.520%	$139.7955	$139.80	$139.80	$139.80
Purchase #3	$244.25	12.341%	$274.3929	$274.39	$274.40	$274.40
Purchase #4	$156.30	12.677%	$176.1142	$176.11	$176.10	$176.10
Purchase #5	$143.66	10.603%	$158.8923	$158.89	$158.90	$158.90
Purchase #6	$152.34	10.174%	$167.8391	$167.84	$167.85	$167.80
Purchase #7	$131.25	4.600%	$137.2875	$137.29	$137.30	$137.30
7 purchase totals =	$1,046.39		$1,144.5870	$1,144.59	$1,144.60	$1,144.60