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	$228.66	11.681%	$255.3698	$255.37	$255.35	$255.40
Purchase #2	$197.53	12.757%	$222.7289	$222.73	$222.75	$222.70
Purchase #3	$141.80	7.854%	$152.937	$152.94	$152.95	$152.90
Purchase #4	$147.58	7.582%	$158.7695	$158.77	$158.75	$158.80
Purchase #5	$127.59	5.742%	$134.9162	$134.92	$134.90	$134.90
Purchase #6	$83.84	13.338%	$95.0226	$95.02	$95.00	$95.00
Purchase #7	$70.69	13.138%	$79.9773	$79.98	$80.00	$80.00
7 purchase totals =	$997.69		$1,099.7213	$1,099.73	$1,099.70	$1,099.70