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	$246.72	13.778%	$280.7131	$280.71	$280.70	$280.70
Purchase #2	$149.68	10.845%	$165.9128	$165.91	$165.90	$165.90
Purchase #3	$20.65	4.686%	$21.6177	$21.62	$21.60	$21.60
Purchase #4	$109.31	9.307%	$119.4835	$119.48	$119.50	$119.50
Purchase #5	$33.81	9.203%	$36.9215	$36.92	$36.90	$36.90
Purchase #6	$168.61	7.268%	$180.8646	$180.86	$180.85	$180.90
Purchase #7	$156.62	5.618%	$165.4189	$165.42	$165.40	$165.40
7 purchase totals =	$885.40		$970.9321	$970.92	$970.85	$970.90