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	$60.66	9.614%	$66.4919	$66.49	$66.50	$66.50
Purchase #2	$237.26	3.651%	$245.9224	$245.92	$245.90	$245.90
Purchase #3	$102.94	8.108%	$111.2864	$111.29	$111.30	$111.30
Purchase #4	$51.91	11.471%	$57.8646	$57.86	$57.85	$57.90
Purchase #5	$204.78	13.835%	$233.1113	$233.11	$233.10	$233.10
Purchase #6	$56.94	8.671%	$61.8773	$61.88	$61.90	$61.90
Purchase #7	$238.88	11.290%	$265.8496	$265.85	$265.85	$265.80
7 purchase totals =	$953.37		$1,042.4035	$1,042.40	$1,042.40	$1,042.40