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	$175.40	6.840%	$187.3974	$187.40	$187.40	$187.40
Purchase #2	$133.30	8.441%	$144.5519	$144.55	$144.55	$144.60
Purchase #3	$6.44	9.756%	$7.0683	$7.07	$7.05	$7.10
Purchase #4	$232.91	10.279%	$256.8508	$256.85	$256.85	$256.90
Purchase #5	$139.75	3.726%	$144.9571	$144.96	$144.95	$145.00
Purchase #6	$232.57	13.308%	$263.5204	$263.52	$263.50	$263.50
Purchase #7	$155.51	8.445%	$168.6428	$168.64	$168.65	$168.60
7 purchase totals =	$1,075.88		$1,172.9887	$1,172.99	$1,172.95	$1,173.10