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	$78.90	13.572%	$89.6083	$89.61	$89.60	$89.60
Purchase #2	$42.47	5.122%	$44.6453	$44.65	$44.65	$44.60
Purchase #3	$225.55	12.721%	$254.2422	$254.24	$254.25	$254.20
Purchase #4	$157.25	9.666%	$172.4498	$172.45	$172.45	$172.40
Purchase #5	$70.97	13.394%	$80.4757	$80.48	$80.50	$80.50
Purchase #6	$12.41	12.641%	$13.9787	$13.98	$14.00	$14.00
Purchase #7	$20.32	5.522%	$21.4421	$21.44	$21.45	$21.40
7 purchase totals =	$607.87		$676.8421	$676.85	$676.90	$676.70