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	$66.75	3.632%	$69.1744	$69.17	$69.15	$69.20
Purchase #2	$52.45	4.350%	$54.7316	$54.73	$54.75	$54.70
Purchase #3	$126.40	12.339%	$141.9965	$142.00	$142.00	$142.00
Purchase #4	$8.42	10.628%	$9.3149	$9.31	$9.30	$9.30
Purchase #5	$137.59	11.852%	$153.8972	$153.90	$153.90	$153.90
Purchase #6	$55.96	5.698%	$59.1486	$59.15	$59.15	$59.10
Purchase #7	$22.89	7.762%	$24.6667	$24.67	$24.65	$24.70
7 purchase totals =	$470.46		$512.9299	$512.93	$512.90	$512.90