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	$73.60	6.620%	$78.4723	$78.47	$78.45	$78.50
Purchase #2	$127.35	11.139%	$141.5355	$141.54	$141.55	$141.50
Purchase #3	$123.55	5.720%	$130.6171	$130.62	$130.60	$130.60
Purchase #4	$63.99	10.297%	$70.5791	$70.58	$70.60	$70.60
Purchase #5	$229.94	11.147%	$255.5714	$255.57	$255.55	$255.60
Purchase #6	$233.73	9.462%	$255.8455	$255.85	$255.85	$255.80
Purchase #7	$105.59	12.317%	$118.5955	$118.60	$118.60	$118.60
7 purchase totals =	$957.75		$1,051.2164	$1,051.23	$1,051.20	$1,051.20