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	$36.37	11.813%	$40.6664	$40.67	$40.65	$40.70
Purchase #2	$59.45	9.749%	$65.2458	$65.25	$65.25	$65.20
Purchase #3	$26.93	11.189%	$29.9432	$29.94	$29.95	$29.90
Purchase #4	$177.77	3.374%	$183.768	$183.77	$183.75	$183.80
Purchase #5	$211.78	7.460%	$227.5788	$227.58	$227.60	$227.60
Purchase #6	$82.94	9.270%	$90.6285	$90.63	$90.65	$90.60
Purchase #7	$48.58	12.811%	$54.8036	$54.80	$54.80	$54.80
7 purchase totals =	$643.82		$692.6343	$692.64	$692.65	$692.60