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	$120.48	10.373%	$132.9774	$132.98	$133.00	$133.00
Purchase #2	$142.85	9.366%	$156.2293	$156.23	$156.25	$156.20
Purchase #3	$80.35	11.235%	$89.3773	$89.38	$89.40	$89.40
Purchase #4	$204.78	8.753%	$222.7044	$222.70	$222.70	$222.70
Purchase #5	$132.76	8.716%	$144.3314	$144.33	$144.35	$144.30
Purchase #6	$49.64	6.641%	$52.9366	$52.94	$52.95	$52.90
Purchase #7	$56.81	12.235%	$63.7607	$63.76	$63.75	$63.80
7 purchase totals =	$787.67		$862.3171	$862.32	$862.40	$862.30