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	$248.87	3.475%	$257.5182	$257.52	$257.50	$257.50
Purchase #2	$228.41	4.131%	$237.8456	$237.85	$237.85	$237.80
Purchase #3	$97.58	8.847%	$106.2129	$106.21	$106.20	$106.20
Purchase #4	$123.72	10.305%	$136.4693	$136.47	$136.45	$136.50
Purchase #5	$192.63	9.470%	$210.8721	$210.87	$210.85	$210.90
Purchase #6	$75.52	4.533%	$78.9433	$78.94	$78.95	$78.90
Purchase #7	$96.96	3.272%	$100.1325	$100.13	$100.15	$100.10
7 purchase totals =	$1,063.69		$1,127.9939	$1,127.99	$1,127.95	$1,127.90