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	$110.65	12.181%	$124.1283	$124.13	$124.15	$124.10
Purchase #2	$128.31	13.694%	$145.8808	$145.88	$145.90	$145.90
Purchase #3	$127.72	10.867%	$141.5993	$141.60	$141.60	$141.60
Purchase #4	$223.79	3.262%	$231.09	$231.09	$231.10	$231.10
Purchase #5	$250.96	3.547%	$259.8616	$259.86	$259.85	$259.90
Purchase #6	$248.78	12.607%	$280.1437	$280.14	$280.15	$280.10
Purchase #7	$171.81	3.873%	$178.4642	$178.46	$178.45	$178.50
7 purchase totals =	$1,262.02		$1,361.1679	$1,361.16	$1,361.20	$1,361.20