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	$229.66	11.324%	$255.6667	$255.67	$255.65	$255.70
Purchase #2	$82.28	4.453%	$85.9439	$85.94	$85.95	$85.90
Purchase #3	$80.56	3.533%	$83.4062	$83.41	$83.40	$83.40
Purchase #4	$207.80	7.259%	$222.8842	$222.88	$222.90	$222.90
Purchase #5	$248.35	9.704%	$272.4499	$272.45	$272.45	$272.40
Purchase #6	$102.47	4.633%	$107.2174	$107.22	$107.20	$107.20
Purchase #7	$186.78	5.107%	$196.3189	$196.32	$196.30	$196.30
7 purchase totals =	$1,137.90		$1,223.8872	$1,223.89	$1,223.85	$1,223.80