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	$6.82	5.874%	$7.2206	$7.22	$7.20	$7.20
Purchase #2	$28.94	12.296%	$32.4985	$32.50	$32.50	$32.50
Purchase #3	$214.72	8.732%	$233.4694	$233.47	$233.45	$233.50
Purchase #4	$163.25	11.773%	$182.4694	$182.47	$182.45	$182.50
Purchase #5	$61.93	7.208%	$66.3939	$66.39	$66.40	$66.40
Purchase #6	$183.94	4.192%	$191.6508	$191.65	$191.65	$191.70
Purchase #7	$203.32	8.828%	$221.2691	$221.27	$221.25	$221.30
7 purchase totals =	$862.92		$934.9717	$934.97	$934.90	$935.10