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	$30.54	8.315%	$33.0794	$33.08	$33.10	$33.10
Purchase #2	$205.70	12.552%	$231.5195	$231.52	$231.50	$231.50
Purchase #3	$213.93	4.828%	$224.2585	$224.26	$224.25	$224.30
Purchase #4	$36.44	6.659%	$38.8665	$38.87	$38.85	$38.90
Purchase #5	$101.64	9.831%	$111.6322	$111.63	$111.65	$111.60
Purchase #6	$127.34	12.194%	$142.8678	$142.87	$142.85	$142.90
Purchase #7	$108.90	10.803%	$120.6645	$120.66	$120.65	$120.70
7 purchase totals =	$824.49		$902.8884	$902.89	$902.85	$903.00