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	$33.86	12.517%	$38.0983	$38.10	$38.10	$38.10
Purchase #2	$153.64	7.177%	$164.6667	$164.67	$164.65	$164.70
Purchase #3	$187.66	9.380%	$205.2625	$205.26	$205.25	$205.30
Purchase #4	$90.63	9.365%	$99.1175	$99.12	$99.10	$99.10
Purchase #5	$247.76	7.587%	$266.5576	$266.56	$266.55	$266.60
Purchase #6	$35.38	8.240%	$38.2953	$38.30	$38.30	$38.30
Purchase #7	$162.50	10.723%	$179.9249	$179.92	$179.90	$179.90
7 purchase totals =	$911.43		$991.9228	$991.93	$991.85	$992.00