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	$248.79	12.593%	$280.1201	$280.12	$280.10	$280.10
Purchase #2	$38.96	6.811%	$41.6136	$41.61	$41.60	$41.60
Purchase #3	$238.73	4.243%	$248.8593	$248.86	$248.85	$248.90
Purchase #4	$219.98	4.693%	$230.3037	$230.30	$230.30	$230.30
Purchase #5	$34.81	9.189%	$38.0087	$38.01	$38.00	$38.00
Purchase #6	$90.52	9.460%	$99.0832	$99.08	$99.10	$99.10
Purchase #7	$159.79	3.515%	$165.4066	$165.41	$165.40	$165.40
7 purchase totals =	$1,031.58		$1,103.3952	$1,103.39	$1,103.35	$1,103.40