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	$227.42	8.554%	$246.8735	$246.87	$246.85	$246.90
Purchase #2	$51.77	10.596%	$57.2555	$57.26	$57.25	$57.30
Purchase #3	$15.99	13.272%	$18.1122	$18.11	$18.10	$18.10
Purchase #4	$89.52	6.828%	$95.6324	$95.63	$95.65	$95.60
Purchase #5	$181.42	3.218%	$187.2581	$187.26	$187.25	$187.30
Purchase #6	$109.39	13.678%	$124.3524	$124.35	$124.35	$124.40
Purchase #7	$56.61	5.807%	$59.8973	$59.90	$59.90	$59.90
7 purchase totals =	$732.12		$789.3814	$789.38	$789.35	$789.50