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	$113.27	13.789%	$128.8888	$128.89	$128.90	$128.90
Purchase #2	$50.30	8.621%	$54.6364	$54.64	$54.65	$54.60
Purchase #3	$132.64	13.303%	$150.2851	$150.29	$150.30	$150.30
Purchase #4	$62.98	4.619%	$65.889	$65.89	$65.90	$65.90
Purchase #5	$236.66	4.181%	$246.5548	$246.55	$246.55	$246.60
Purchase #6	$220.98	7.828%	$238.2783	$238.28	$238.30	$238.30
Purchase #7	$143.98	12.291%	$161.6766	$161.68	$161.70	$161.70
7 purchase totals =	$960.81		$1,046.2090	$1,046.22	$1,046.30	$1,046.30