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	$133.87	7.361%	$143.7242	$143.72	$143.70	$143.70
Purchase #2	$180.76	10.716%	$200.1302	$200.13	$200.15	$200.10
Purchase #3	$101.86	10.764%	$112.8242	$112.82	$112.80	$112.80
Purchase #4	$216.80	7.820%	$233.7538	$233.75	$233.75	$233.80
Purchase #5	$249.60	12.346%	$280.4156	$280.42	$280.40	$280.40
Purchase #6	$226.28	4.434%	$236.3133	$236.31	$236.30	$236.30
Purchase #7	$81.63	9.320%	$89.2379	$89.24	$89.25	$89.20
7 purchase totals =	$1,190.80		$1,296.3992	$1,296.39	$1,296.35	$1,296.30