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	$47.74	12.114%	$53.5232	$53.52	$53.50	$53.50
Purchase #2	$136.78	11.464%	$152.4605	$152.46	$152.45	$152.50
Purchase #3	$17.51	5.382%	$18.4524	$18.45	$18.45	$18.50
Purchase #4	$209.62	12.340%	$235.4871	$235.49	$235.50	$235.50
Purchase #5	$156.29	11.339%	$174.0117	$174.01	$174.00	$174.00
Purchase #6	$52.66	5.572%	$55.5942	$55.59	$55.60	$55.60
Purchase #7	$156.74	13.109%	$177.287	$177.29	$177.30	$177.30
7 purchase totals =	$777.34		$866.8161	$866.81	$866.80	$866.90