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	$47.73	10.771%	$52.871	$52.87	$52.85	$52.90
Purchase #2	$38.77	12.418%	$43.5845	$43.58	$43.60	$43.60
Purchase #3	$162.96	12.825%	$183.8596	$183.86	$183.85	$183.90
Purchase #4	$175.59	7.297%	$188.4028	$188.40	$188.40	$188.40
Purchase #5	$51.59	8.807%	$56.1335	$56.13	$56.15	$56.10
Purchase #6	$119.65	7.752%	$128.9253	$128.93	$128.95	$128.90
Purchase #7	$187.61	9.708%	$205.8232	$205.82	$205.80	$205.80
7 purchase totals =	$783.90		$859.5999	$859.59	$859.60	$859.60