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	$134.57	3.556%	$139.3553	$139.36	$139.35	$139.40
Purchase #2	$71.25	10.607%	$78.8075	$78.81	$78.80	$78.80
Purchase #3	$73.88	12.328%	$82.9879	$82.99	$83.00	$83.00
Purchase #4	$31.79	8.538%	$34.5042	$34.50	$34.50	$34.50
Purchase #5	$95.36	5.400%	$100.5094	$100.51	$100.50	$100.50
Purchase #6	$138.42	9.483%	$151.5464	$151.55	$151.55	$151.50
Purchase #7	$61.45	10.606%	$67.9674	$67.97	$67.95	$68.00
7 purchase totals =	$606.72		$655.6781	$655.69	$655.65	$655.70