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	$223.63	11.536%	$249.428	$249.43	$249.45	$249.40
Purchase #2	$197.54	12.239%	$221.7169	$221.72	$221.70	$221.70
Purchase #3	$5.80	11.392%	$6.4607	$6.46	$6.45	$6.50
Purchase #4	$116.43	4.618%	$121.8067	$121.81	$121.80	$121.80
Purchase #5	$94.55	11.749%	$105.6587	$105.66	$105.65	$105.70
Purchase #6	$38.79	13.198%	$43.9095	$43.91	$43.90	$43.90
Purchase #7	$222.38	12.693%	$250.6067	$250.61	$250.60	$250.60
7 purchase totals =	$899.12		$999.5872	$999.60	$999.55	$999.60