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	$128.61	11.590%	$143.5159	$143.52	$143.50	$143.50
Purchase #2	$16.71	11.611%	$18.6502	$18.65	$18.65	$18.70
Purchase #3	$128.74	8.659%	$139.8876	$139.89	$139.90	$139.90
Purchase #4	$172.82	10.477%	$190.9264	$190.93	$190.95	$190.90
Purchase #5	$95.28	9.795%	$104.6127	$104.61	$104.60	$104.60
Purchase #6	$122.73	9.387%	$134.2507	$134.25	$134.25	$134.30
Purchase #7	$79.52	8.523%	$86.2975	$86.30	$86.30	$86.30
7 purchase totals =	$744.41		$818.1410	$818.15	$818.15	$818.20