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	$127.46	9.282%	$139.2908	$139.29	$139.30	$139.30
Purchase #2	$85.97	9.222%	$93.8982	$93.90	$93.90	$93.90
Purchase #3	$123.58	10.456%	$136.5015	$136.50	$136.50	$136.50
Purchase #4	$238.80	8.416%	$258.8974	$258.90	$258.90	$258.90
Purchase #5	$237.83	8.498%	$258.0408	$258.04	$258.05	$258.00
Purchase #6	$144.38	7.728%	$155.5377	$155.54	$155.55	$155.50
Purchase #7	$12.73	4.625%	$13.3188	$13.32	$13.30	$13.30
7 purchase totals =	$970.75		$1,055.4852	$1,055.49	$1,055.50	$1,055.40