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	$82.54	8.577%	$89.6195	$89.62	$89.60	$89.60
Purchase #2	$167.81	3.189%	$173.1615	$173.16	$173.15	$173.20
Purchase #3	$79.90	7.385%	$85.8006	$85.80	$85.80	$85.80
Purchase #4	$156.79	9.747%	$172.0723	$172.07	$172.05	$172.10
Purchase #5	$15.81	12.108%	$17.7243	$17.72	$17.70	$17.70
Purchase #6	$195.43	13.204%	$221.2346	$221.23	$221.25	$221.20
Purchase #7	$72.64	11.459%	$80.9638	$80.96	$80.95	$81.00
7 purchase totals =	$770.92		$840.5766	$840.56	$840.50	$840.60