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	$38.26	12.817%	$43.1638	$43.16	$43.15	$43.20
Purchase #2	$132.70	8.129%	$143.4872	$143.49	$143.50	$143.50
Purchase #3	$130.97	10.422%	$144.6197	$144.62	$144.60	$144.60
Purchase #4	$128.48	10.683%	$142.2055	$142.21	$142.20	$142.20
Purchase #5	$36.76	9.266%	$40.1662	$40.17	$40.15	$40.20
Purchase #6	$73.67	6.106%	$78.1683	$78.17	$78.15	$78.20
Purchase #7	$205.87	10.570%	$227.6305	$227.63	$227.65	$227.60
7 purchase totals =	$746.71		$819.4412	$819.45	$819.40	$819.50