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	$155.45	9.561%	$170.3126	$170.31	$170.30	$170.30
Purchase #2	$103.90	7.610%	$111.8068	$111.81	$111.80	$111.80
Purchase #3	$86.70	8.296%	$93.8926	$93.89	$93.90	$93.90
Purchase #4	$123.72	13.157%	$139.9978	$140.00	$140.00	$140.00
Purchase #5	$156.71	3.158%	$161.6589	$161.66	$161.65	$161.70
Purchase #6	$96.42	5.337%	$101.5659	$101.57	$101.55	$101.60
Purchase #7	$133.57	12.705%	$150.5401	$150.54	$150.55	$150.50
7 purchase totals =	$856.47		$929.7747	$929.78	$929.75	$929.80