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	$200.46	13.208%	$226.9368	$226.94	$226.95	$226.90
Purchase #2	$109.72	3.533%	$113.5964	$113.60	$113.60	$113.60
Purchase #3	$122.91	12.466%	$138.232	$138.23	$138.25	$138.20
Purchase #4	$89.27	11.111%	$99.1888	$99.19	$99.20	$99.20
Purchase #5	$86.83	3.836%	$90.1608	$90.16	$90.15	$90.20
Purchase #6	$89.72	6.293%	$95.3661	$95.37	$95.35	$95.40
Purchase #7	$102.97	13.752%	$117.1304	$117.13	$117.15	$117.10
7 purchase totals =	$801.88		$880.6113	$880.62	$880.65	$880.60