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	$36.70	9.146%	$40.0566	$40.06	$40.05	$40.10
Purchase #2	$62.61	4.568%	$65.47	$65.47	$65.45	$65.50
Purchase #3	$143.38	8.376%	$155.3895	$155.39	$155.40	$155.40
Purchase #4	$72.34	13.108%	$81.8223	$81.82	$81.80	$81.80
Purchase #5	$72.86	4.340%	$76.0221	$76.02	$76.00	$76.00
Purchase #6	$250.50	11.607%	$279.5755	$279.58	$279.60	$279.60
Purchase #7	$59.61	5.398%	$62.8277	$62.83	$62.85	$62.80
7 purchase totals =	$698.00		$761.1637	$761.17	$761.15	$761.20