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	$119.38	3.800%	$123.9164	$123.92	$123.90	$123.90
Purchase #2	$111.74	5.443%	$117.822	$117.82	$117.80	$117.80
Purchase #3	$206.78	9.693%	$226.8232	$226.82	$226.80	$226.80
Purchase #4	$51.98	9.492%	$56.9139	$56.91	$56.90	$56.90
Purchase #5	$86.78	5.631%	$91.6666	$91.67	$91.65	$91.70
Purchase #6	$76.26	6.804%	$81.4487	$81.45	$81.45	$81.40
Purchase #7	$82.57	3.165%	$85.1833	$85.18	$85.20	$85.20
7 purchase totals =	$735.49		$783.7741	$783.77	$783.70	$783.70