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	$136.79	5.838%	$144.7758	$144.78	$144.80	$144.80
Purchase #2	$198.70	6.315%	$211.2479	$211.25	$211.25	$211.20
Purchase #3	$159.28	8.568%	$172.9271	$172.93	$172.95	$172.90
Purchase #4	$214.89	4.469%	$224.4934	$224.49	$224.50	$224.50
Purchase #5	$48.32	10.222%	$53.2593	$53.26	$53.25	$53.30
Purchase #6	$227.89	13.712%	$259.1383	$259.14	$259.15	$259.10
Purchase #7	$159.42	9.688%	$174.8646	$174.86	$174.85	$174.90
7 purchase totals =	$1,145.29		$1,240.7064	$1,240.71	$1,240.75	$1,240.70