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	$34.92	10.589%	$38.6177	$38.62	$38.60	$38.60
Purchase #2	$161.89	10.571%	$179.0034	$179.00	$179.00	$179.00
Purchase #3	$128.35	8.674%	$139.4831	$139.48	$139.50	$139.50
Purchase #4	$53.90	10.535%	$59.5784	$59.58	$59.60	$59.60
Purchase #5	$217.26	7.410%	$233.359	$233.36	$233.35	$233.40
Purchase #6	$52.92	8.339%	$57.333	$57.33	$57.35	$57.30
Purchase #7	$200.86	12.641%	$226.2507	$226.25	$226.25	$226.30
7 purchase totals =	$850.10		$933.6253	$933.62	$933.65	$933.70