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	$151.26	3.752%	$156.9353	$156.94	$156.95	$156.90
Purchase #2	$135.94	3.235%	$140.3377	$140.34	$140.35	$140.30
Purchase #3	$39.58	8.482%	$42.9372	$42.94	$42.95	$42.90
Purchase #4	$62.33	5.212%	$65.5786	$65.58	$65.60	$65.60
Purchase #5	$39.63	9.458%	$43.3782	$43.38	$43.40	$43.40
Purchase #6	$70.65	12.563%	$79.5258	$79.53	$79.55	$79.50
Purchase #7	$99.78	11.302%	$111.0571	$111.06	$111.05	$111.10
7 purchase totals =	$599.17		$639.7499	$639.77	$639.85	$639.70