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	$139.47	11.862%	$156.0139	$156.01	$156.00	$156.00
Purchase #2	$52.98	5.351%	$55.815	$55.82	$55.80	$55.80
Purchase #3	$111.74	5.848%	$118.2746	$118.27	$118.25	$118.30
Purchase #4	$49.51	3.822%	$51.4023	$51.40	$51.40	$51.40
Purchase #5	$245.32	7.557%	$263.8588	$263.86	$263.85	$263.90
Purchase #6	$59.50	12.633%	$67.0166	$67.02	$67.00	$67.00
Purchase #7	$139.94	3.275%	$144.523	$144.52	$144.50	$144.50
7 purchase totals =	$798.46		$856.9042	$856.90	$856.80	$856.90