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	$53.45	8.431%	$57.9564	$57.96	$57.95	$58.00
Purchase #2	$224.90	6.820%	$240.2382	$240.24	$240.25	$240.20
Purchase #3	$99.38	9.218%	$108.5408	$108.54	$108.55	$108.50
Purchase #4	$91.70	13.333%	$103.9264	$103.93	$103.95	$103.90
Purchase #5	$45.28	10.723%	$50.1354	$50.14	$50.15	$50.10
Purchase #6	$88.78	11.622%	$99.098	$99.10	$99.10	$99.10
Purchase #7	$237.28	12.782%	$267.6091	$267.61	$267.60	$267.60
7 purchase totals =	$840.77		$927.5043	$927.52	$927.55	$927.40