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	$174.95	9.758%	$192.0216	$192.02	$192.00	$192.00
Purchase #2	$45.60	13.425%	$51.7218	$51.72	$51.70	$51.70
Purchase #3	$173.49	10.593%	$191.8678	$191.87	$191.85	$191.90
Purchase #4	$196.94	12.717%	$221.9849	$221.98	$222.00	$222.00
Purchase #5	$42.76	6.123%	$45.3782	$45.38	$45.40	$45.40
Purchase #6	$20.37	6.378%	$21.6692	$21.67	$21.65	$21.70
Purchase #7	$110.26	3.610%	$114.2404	$114.24	$114.25	$114.20
7 purchase totals =	$764.37		$838.8839	$838.88	$838.85	$838.90