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	$242.43	5.436%	$255.6085	$255.61	$255.60	$255.60
Purchase #2	$45.83	11.641%	$51.1651	$51.17	$51.15	$51.20
Purchase #3	$221.46	7.154%	$237.3032	$237.30	$237.30	$237.30
Purchase #4	$249.46	12.596%	$280.882	$280.88	$280.90	$280.90
Purchase #5	$220.85	7.762%	$237.9924	$237.99	$238.00	$238.00
Purchase #6	$26.98	13.342%	$30.5797	$30.58	$30.60	$30.60
Purchase #7	$116.51	11.821%	$130.2826	$130.28	$130.30	$130.30
7 purchase totals =	$1,123.52		$1,223.8135	$1,223.81	$1,223.85	$1,223.90