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	$111.90	7.128%	$119.8762	$119.88	$119.90	$119.90
Purchase #2	$36.29	3.413%	$37.5286	$37.53	$37.55	$37.50
Purchase #3	$231.30	10.255%	$255.0198	$255.02	$255.00	$255.00
Purchase #4	$140.47	12.566%	$158.1215	$158.12	$158.10	$158.10
Purchase #5	$108.96	13.153%	$123.2915	$123.29	$123.30	$123.30
Purchase #6	$80.54	11.786%	$90.0324	$90.03	$90.05	$90.00
Purchase #7	$64.58	9.273%	$70.5685	$70.57	$70.55	$70.60
7 purchase totals =	$774.04		$854.4385	$854.44	$854.45	$854.40