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	$143.58	6.492%	$152.9012	$152.90	$152.90	$152.90
Purchase #2	$83.62	8.561%	$90.7787	$90.78	$90.80	$90.80
Purchase #3	$22.87	7.471%	$24.5786	$24.58	$24.60	$24.60
Purchase #4	$133.42	3.559%	$138.1684	$138.17	$138.15	$138.20
Purchase #5	$104.79	9.650%	$114.9022	$114.90	$114.90	$114.90
Purchase #6	$167.27	9.403%	$182.9984	$183.00	$183.00	$183.00
Purchase #7	$49.37	6.517%	$52.5874	$52.59	$52.60	$52.60
7 purchase totals =	$704.92		$756.9149	$756.92	$756.95	$757.00