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	$135.63	6.195%	$144.0323	$144.03	$144.05	$144.00
Purchase #2	$59.83	13.473%	$67.8909	$67.89	$67.90	$67.90
Purchase #3	$102.45	9.266%	$111.943	$111.94	$111.95	$111.90
Purchase #4	$148.59	5.700%	$157.0596	$157.06	$157.05	$157.10
Purchase #5	$17.26	11.584%	$19.2594	$19.26	$19.25	$19.30
Purchase #6	$178.77	10.168%	$196.9473	$196.95	$196.95	$196.90
Purchase #7	$119.91	12.281%	$134.6361	$134.64	$134.65	$134.60
7 purchase totals =	$762.44		$831.7686	$831.77	$831.80	$831.70