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	$230.27	11.550%	$256.8662	$256.87	$256.85	$256.90
Purchase #2	$146.33	7.245%	$156.9316	$156.93	$156.95	$156.90
Purchase #3	$173.29	4.604%	$181.2683	$181.27	$181.25	$181.30
Purchase #4	$162.78	4.780%	$170.5609	$170.56	$170.55	$170.60
Purchase #5	$62.45	8.716%	$67.8931	$67.89	$67.90	$67.90
Purchase #6	$188.50	10.718%	$208.7034	$208.70	$208.70	$208.70
Purchase #7	$168.72	7.601%	$181.5444	$181.54	$181.55	$181.50
7 purchase totals =	$1,132.34		$1,223.7679	$1,223.76	$1,223.75	$1,223.80