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	$228.42	9.121%	$249.2542	$249.25	$249.25	$249.30
Purchase #2	$145.38	7.204%	$155.8532	$155.85	$155.85	$155.90
Purchase #3	$212.86	12.451%	$239.3632	$239.36	$239.35	$239.40
Purchase #4	$60.39	10.667%	$66.8318	$66.83	$66.85	$66.80
Purchase #5	$82.42	8.759%	$89.6392	$89.64	$89.65	$89.60
Purchase #6	$25.50	8.325%	$27.6229	$27.62	$27.60	$27.60
Purchase #7	$241.99	11.519%	$269.8648	$269.86	$269.85	$269.90
7 purchase totals =	$996.96		$1,098.4293	$1,098.41	$1,098.40	$1,098.50