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	$52.85	12.555%	$59.4853	$59.49	$59.50	$59.50
Purchase #2	$109.82	6.367%	$116.8122	$116.81	$116.80	$116.80
Purchase #3	$88.63	11.102%	$98.4697	$98.47	$98.45	$98.50
Purchase #4	$87.92	13.143%	$99.4753	$99.48	$99.50	$99.50
Purchase #5	$234.59	5.522%	$247.5441	$247.54	$247.55	$247.50
Purchase #6	$21.69	9.131%	$23.6705	$23.67	$23.65	$23.70
Purchase #7	$194.46	10.639%	$215.1486	$215.15	$215.15	$215.10
7 purchase totals =	$789.96		$860.6057	$860.61	$860.60	$860.60