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	$5.25	8.135%	$5.6771	$5.68	$5.70	$5.70
Purchase #2	$95.64	4.123%	$99.5832	$99.58	$99.60	$99.60
Purchase #3	$59.98	8.192%	$64.8936	$64.89	$64.90	$64.90
Purchase #4	$162.72	10.272%	$179.4346	$179.43	$179.45	$179.40
Purchase #5	$18.92	8.380%	$20.5055	$20.51	$20.50	$20.50
Purchase #6	$231.69	7.264%	$248.52	$248.52	$248.50	$248.50
Purchase #7	$47.64	10.583%	$52.6817	$52.68	$52.70	$52.70
7 purchase totals =	$621.84		$671.2957	$671.29	$671.35	$671.30