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	$99.94	9.800%	$109.7341	$109.73	$109.75	$109.70
Purchase #2	$41.97	4.798%	$43.9837	$43.98	$44.00	$44.00
Purchase #3	$10.98	11.605%	$12.2542	$12.25	$12.25	$12.30
Purchase #4	$28.93	10.814%	$32.0585	$32.06	$32.05	$32.10
Purchase #5	$193.49	13.750%	$220.0949	$220.09	$220.10	$220.10
Purchase #6	$87.73	4.269%	$91.4752	$91.48	$91.50	$91.50
Purchase #7	$69.60	12.573%	$78.3508	$78.35	$78.35	$78.40
7 purchase totals =	$532.64		$587.9514	$587.94	$588.00	$588.10