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	$53.67	6.462%	$57.1382	$57.14	$57.15	$57.10
Purchase #2	$144.87	9.484%	$158.6095	$158.61	$158.60	$158.60
Purchase #3	$202.90	9.455%	$222.0842	$222.08	$222.10	$222.10
Purchase #4	$143.68	9.190%	$156.8842	$156.88	$156.90	$156.90
Purchase #5	$228.90	12.637%	$257.8261	$257.83	$257.85	$257.80
Purchase #6	$43.44	12.635%	$48.9286	$48.93	$48.95	$48.90
Purchase #7	$208.54	6.239%	$221.5508	$221.55	$221.55	$221.60
7 purchase totals =	$1,026.00		$1,123.0216	$1,123.02	$1,123.10	$1,123.00