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	$140.27	3.209%	$144.7713	$144.77	$144.75	$144.80
Purchase #2	$64.71	4.152%	$67.3968	$67.40	$67.40	$67.40
Purchase #3	$167.38	3.615%	$173.4308	$173.43	$173.45	$173.40
Purchase #4	$36.37	6.772%	$38.833	$38.83	$38.85	$38.80
Purchase #5	$179.39	12.863%	$202.4649	$202.46	$202.45	$202.50
Purchase #6	$82.30	9.201%	$89.8724	$89.87	$89.85	$89.90
Purchase #7	$248.67	13.607%	$282.5065	$282.51	$282.50	$282.50
7 purchase totals =	$919.09		$999.2757	$999.27	$999.25	$999.30