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	$9.45	11.598%	$10.546	$10.55	$10.55	$10.50
Purchase #2	$9.49	13.300%	$10.7522	$10.75	$10.75	$10.80
Purchase #3	$42.64	13.526%	$48.4075	$48.41	$48.40	$48.40
Purchase #4	$17.41	10.801%	$19.2905	$19.29	$19.30	$19.30
Purchase #5	$22.93	7.227%	$24.5872	$24.59	$24.60	$24.60
Purchase #6	$54.70	5.214%	$57.5521	$57.55	$57.55	$57.60
Purchase #7	$101.79	7.415%	$109.3377	$109.34	$109.35	$109.30
7 purchase totals =	$258.41		$280.4732	$280.48	$280.50	$280.50