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	$130.54	4.462%	$136.3647	$136.36	$136.35	$136.40
Purchase #2	$204.54	8.734%	$222.4045	$222.40	$222.40	$222.40
Purchase #3	$242.49	12.230%	$272.1465	$272.15	$272.15	$272.10
Purchase #4	$229.75	11.251%	$255.5992	$255.60	$255.60	$255.60
Purchase #5	$136.78	6.149%	$145.1906	$145.19	$145.20	$145.20
Purchase #6	$62.29	4.768%	$65.26	$65.26	$65.25	$65.30
Purchase #7	$176.70	11.391%	$196.8279	$196.83	$196.85	$196.80
7 purchase totals =	$1,183.09		$1,293.7934	$1,293.79	$1,293.80	$1,293.80